 Principles of Geology, Chapter 14, Part 2. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, visit LibriVox.org. The Principles of Geology by Charles Lyle. Newly formed valleys. In traveling in Georgia and Alabama in 1846, I saw in both those states the commencement of hundreds of valleys in places where the native forest had recently been removed. One of these newly formed gullies or ravines is represented in the annexed woodcut, figure 14, from a drawing which I made on the spot. It occurs three miles and a half due west of Millageville, the capital of Georgia, and is situated on the farm of Funmona, on the direct road to Macon. Twenty years ago, before the land was cleared, it had no existence, but when the trees of the forest were cut down, cracks three feet deep were caused by the sun's heat in the clay, and during the rains, a sudden rush of water through the principal crack deepened it at its lowest extremity, from whence the excavating power worked backwards, till in the course of twenty years, a chasm measuring no less than 55 feet in depth, 300 yards in length, and varying in width from 20 to 180 feet was the result. The high road has been several times turned to avoid this cavity, the enlargement of which is still proceeding, and the old line of road may be seen to have held its course directly over what is now the wildest part of the ravine. In the perpendicular walls of this great chasm appear beds of clay and sand, red, white, yellow, and green, produced by the decomposition in-city of Hornblendic Gnaeus, with layers and veins of quartz, which remain entire, to prove that the whole mass was once solid and crystalline. I infer, from the rapidity of the denudation, which only began here after the removal of the native wood, that this spot, elevated about 600 feet above the sea, has been always covered with a dense forest from the remote time when it first emerged from the sea. The termination of the cavity on the right hand, in the foreground, is the head or upper end of the ravine, and in almost every case such gullies are lengthened by the streams cutting their way backwards. The depth of the upper end is often, as in this case, considerable, and there is usually at this point, during floods, a small cascade, sinuosities of rivers. In proportion as such valleys are widened, sinuosities are caused by the deflection of the stream, first to one side, and then to the other. The unequal hardness of the materials through which the channel is eroded tends partly to give new directions to the lateral force of excavation. When by these, or by accidental shiftings of the alluvial matter in the channel, the current is made to cross its current line of descent, it eats out a curve in the opposite bank, or in the side of the hills, bounding the valley, from which curve it is turned back again at an equal angle so that it recrosses the line of descent, and gradually hollows out, another curve lower down in the opposite bank, till the whole, sides of the valley, or riverbed, present a succession of salient and retiring angles. Among the causes of deviation from a straight course, by which torrents and rivers tend in mountainous regions to widen the valleys through which they flow, may be mentioned the confluence of lateral torrents, swollen irregularly at different seasons by partial storms, and discharging at different times unequal quantities of sand, mud, and pebbles into the main channel. When the tortuous flexures of a river are extremely great, as often happens in alluvial planes, the aberration from the direct line of descent may be restored by the river, cutting through the isthmus, which separates two neighboring curves. Thus in the annex diagram, the extreme sinuosity of the river has caused it to return for a brief space in a contrary direction to its main course, so that a peninsula is formed, and the isthmus, at A, is consumed on both sides by currents flowing in opposite directions. In this case, an island is soon formed, on either side of which a portion of the stream usually remains. Transporting Power of Water In regard to the transporting power of water, we may often be surprised at the facility with which streams of a small size, and descending a slight declivity, bear along coarse sand and gravel, for we usually estimate the weight of rocks in air and do not reflect on their comparative buoyancy when submerged in a denser fluid. The specific gravity of many rocks is not more than twice that of water, and very rarely more than thrice, so that almost all the fragments propelled by a stream have lost a third, and many of them a half, of what we usually term their weight. It has been proved by experiment, in contradiction to the theories of the earlier writers on hydrostatics, to be a universal law regulating the motion of running water, that the velocity at the bottom of the stream is everywhere less than in any part above it, and is greatest at the surface. Also that the superficial particles in the middle of the stream move swifter than those at the sides. This retardation of the lowest and lateral currents is produced by friction, and when the velocity is sufficiently great, the soil composing the sides and bottom gives way. A velocity of 3 inches per second at the bottom is ascertained to be sufficient to tear up fine clay, 6 inches per second, fine sand, 12 inches per second, fine gravel, and 3 feet per second, stones of the size of an egg. When this mechanical power of running water is considered, we are prepared for the transportation before alluded to, of large quantities of gravel, sand, and mud by torrents which descend from mountainous regions, but a question naturally arises, how the more tranquil rivers of the valleys and plains flowing on comparatively level ground can remove the prodigious burden which is discharged into them by their numerous tributaries, and by what means they are enabled to convey the whole mass to the sea. If they had not this removing power, their channels would be annually choked up, and the valleys of the lower country and plains at the base of mountain chains would be continually strewn over with fragments of rock and sterile sand, but this evil is prevented by a general law regulating the conduct of running water, that two equal streams do not when united occupy a bed of double service. Nay, the width of the principal river, after the junction of a tributary, sometimes remains the same as before, or is even lessened. The cause of this apparent paradox was long ago explained by the Italian writers, who had studied the confluence of the Poe and its feeders in the plains of Lombardy. The addition of a smaller river augments the velocity of the main stream, often in the same proportion as it does the quantity of water, thus the Venetian branch of the Poe swallowed up the Faranese branch, and that of Panero, without any enlargement of its own dimensions. The cause of the greater velocity is, first, that after the union of two rivers, the water, in place of the friction of four shores, has only that of two to surmount. Secondly, because the main body of the stream being farther distant from the banks, flows on with less interruption, and lastly, because a greater quantity of water moving more swiftly digs deeper into the river's bed. By this beautiful adjustment, the water which drains the interior country is made continually to occupy less room as it approaches the sea, and thus the most valuable part of our continents, the rich deltas and great alluvial plains, are prevented from being constantly under water. River floods in Scotland, 1829. Many remarkable illustrations of the power of running water in moving stones and heavy materials were afforded by the storm and floods, which occurred on the 3rd and 4th of August, 1829, in Aberdeenshire, and other counties in Scotland. The elements during this storm assumed all the characters which marked the tropical hurricanes, the wind blowing in sudden gusts and whirlwinds, the lightning and thunder being such as is rarely witnessed in our climate, and heavy rain falling without intermission. The floods extended almost simultaneously and with equal violence over that part of the northeast of Scotland, which would be cut off by two lines drawn from the head of Loughranaw. One towards Inverness and the other to Stonehaven. The united line of the different rivers which were flooded could not be less than from five to seven hundred miles in length, and the whole of their courses were marked by the destruction of bridges, roads, crops and buildings. Sir T.D. Louder has recorded the destruction of thirty-eight bridges and the entire obliteration of a great number of farms and hamlets. On the Nairn, a fragment of sandstone, fourteen feet long by three feet wide and one foot thick, was carried above two hundred yards down the river. Some new ravines were formed on the sides of mountains where no streams had previously flowed, and ancient river channels which had never been filled from time immemorial gave passage to a copious flood. The bridge over the D at Balleterre consisted of five arches, having upon the whole a waterway of two hundred and sixty feet. The bed of the river, on which the piers rested, was composed of rolled pieces of granite and guineas. The bridge was built of granite and had stood uninjured for twenty years, but the different parts were swept away in succession by the flood, and the whole mass of masonry disappeared in the bed of the river. The river Don, observes Mr. Far Carson in his account of the inundations, has upon my own premises forced a mass of four or five hundred tons of stones, many of them two or three hundred pounds weight, up an inclined plain, rising six feet in eight or ten yards, and left them in a retangular heap about three feet deep on a flat ground. The heap ends abruptly at its lower extremity. The power even of a small rivulet, when swollen by rain in removing heavy bodies, was exemplified in August 1827 in the college, a small stream which flows at a slight declivity from the eastern watershed of the Chevyot Hills. Several thousand tons weight of gravel and sand were transported to the plain of the till, and a bridge, then in progress of building, was carried away, some of the archstones of which, weighing from half to three quarters of a ton each, were propelled two miles down the rivulet. On the same occasion, the current tore away from the abutment of a mill dam a large block of greenstone porphyry, weighing nearly two tons, and transported it to the distance of a quarter of a mile. Instances are related, as occurring repeatedly, in which from one to three thousand tons of gravel are, in like manner, removed by this streamlet to still greater distances in one day. Floods Caused by Landslips 1826 The power which running water may exert in the laps of ages, in widening and deepening a valley, does not so much depend on the volume and velocity of the stream usually flowing in it, but on the number and magnitude of the obstructions which have different periods opposed its free passage. If a torrent, however small, be effectually dammed up, the size of the valley above the barrier and its declivity below are not the dimensions of the torrent, will determine the violence of the debacle. If a torrent, however small, be effectually dammed up, the size of the valley above the barrier and its declivity below, and not the dimensions of the torrent, will determine the violence of the debacle. The most universal source of local deluges are landslips, slides, or avalanches, as they are sometimes called, when great masses of rock and soil, or sometimes ice and snow, are precipitated into the bed of a river, the boundary cliffs of which have been thrown down by the shock of an earthquake, or undermined by springs or other causes. Volumes might be filled with the enumeration of instances on record of these terrific catastrophes. I shall therefore select a few examples of recent occurrence, the facts of which are well authenticated. Two dry seasons in the White Mountains in New Hampshire, United States, were followed by heavy rains on the 28th of August, 1826, when from the steep and lofty declivities which rise abruptly on both sides of the River Sacco, innumerable rocks and stones, many of sufficient size to fill a common apartment, were detached and in their descent swept down before them in one promiscuous and frightful ruin, forests, shrubs, and the earth which sustained them. Although there are numerous indications on the steep sides of these hills of former slides of the same kind, yet no tradition had been handed down of any similar catastrophe within the memory of man, and the growth of the forest on the very spots now devastated, clearly showed that for a long interval nothing similar had occurred. One of these moving masses was afterwards found to have slid three miles with an average breadth of a quarter of a mile. The natural excavations commenced generally in a trench a few yards in depth and a few rods in width, and descended the mountains, widening and deepening, till they became vast chasms. At the base of these hollow ravines was seen a confused mass of ruins consisting of transported earth, gravel, rocks, and trees. Forests of spruce fir and hemlock, a kind of fir somewhat resembling our you in foliage, were prostrated with as much ease as if they had been fields of grain, for where they disputed the ground, the torrent of mud and rock accumulated behind, till it gathered sufficient force to burst the temporary barrier. The valleys of the Amanusuk and Sacco presented, for many miles, an uninterrupted scene of desolation, all the bridges being carried away as well as those over their tributary streams. In some places the road was excavated to a depth of from 15 to 20 feet. In others it was covered with earth, rocks, and trees to as great a height. The water flowed for many weeks after the flood, as densely charged with earth as it could be without being changed into mud, and marks were seen in various localities of its having risen on either side of the valley to more than 25 feet above its ordinary level. Many sheep and cattle were swept away, and the willy family, nine in number, who in alarm had deserted their house, were destroyed on the banks of the Sacco, seven of their mangled bodies were afterwards found near the river, buried beneath driftwood and mountain ruins. 11 years after the event, the deep channels worn by the avalanches of mud and stone, and the immense heaps of boulders and blocks of granite in the river channel, still formed, says Professor Hubbard, a picturesque feature of the scenery. When I visited the country in 1845, eight years after Professor Hubbard, I found the signs of devastation still very striking. I also particularly remarked that although the surface of the bare granitic rocks had been smoothed by the passage over them of so much mud and stone, there were no continuous parallel and rectilinear furrows, nor any of the fine scratches or streye which characterized glacial action. The absence of these is nowhere more clearly exemplified than in the bare rocks over which passed the great willy slide of 1826. But the catastrophes in the white mountains were insignificant when compared to those which are occasioned by earthquakes, when the boundary hills, for miles in length, are thrown down into the hollow of a valley. I shall have opportunities of alluding to inundations of this kind when treating expressly of earthquakes, and shall content myself at present with selecting an example of a flood due to a different cause. Flood in the Valley of Ben, 1818. The Valley of Ben is one of the largest of the lateral embranchments of the main valley of the Rhone, above the lake of Geneva. Its upper portion was in 1818 converted into a lake by the damming up of a narrow pass by avalanches of snow and ice precipitated from an elevated glacier into the bed of the river Dransa. In the winter season, during continued frost, scarcely any water flows in the bed of this river to preserve an open channel so that the ice barrier remained entire until the melting of the snows in spring, when a lake was formed above about half a league in length, which finally attained in some parts a depth of about 200 feet and a width of about 700 feet. To prevent or lessen the mischief apprehended from the sudden bursting of the barrier, an artificial gallery, 700 feet in length, was cut through the ice before the waters had risen to a great height. When at length they accumulated and flowed through this tunnel, they dissolved the ice and thus deepened their channel until nearly half of the whole contents of the lake were slowly drained off. But at length, on the approach of the hot season, the central portion of the remaining mass of ice gave way with a tremendous crash, and the residue of the lake was emptied in half an hour. In the course of its descent, the waters encountered several narrow gorges, and at each of these they rose to a great height and then burst with new violence into the next basin, sweeping along rocks, forests, houses, bridges, and cultivated land. For the greater part of its course, the flood resembled a moving mass of rock and mud rather than of water. Some fragments of granitic rocks of enormous magnitude, and which from their dimensions might be compared without exaggeration to houses, were torn out of a more ancient Eluvian and borne down for a quarter of a mile. One of the fragments moved was 60 paces in circumference. The velocity of the water in the first part of its course was 33 feet per second, which diminished to six feet before it reached the lake of Geneva, where it arrived in six hours and a half, the distance being 45 miles. This flood left behind it on the plains of Martigny, thousands of trees torn up by the roots, together with the ruins of buildings. Some of the houses in that town were filled with mud up to the second story. After expanding in the plain of Martigny, it entered the Rhône and did no further damage, but some bodies of men who had been drowned above Martigny were afterwards found at the distance of about 30 miles, floating on the larger side of the lake of Geneva, near Veve. The waters, on escaping from the temporary lake, intermixed with mud and rock, swept along for the first four miles at the rate of about 20 miles an hour, and Monsieur Escher, the engineer, calculated that the flood furnished 300,000 cubic feet of water every second, an efflux which is five times greater than that of the Rhône below Basel. Now, if part of the lake had not been gradually drained off, the flood would have been nearly double, approaching in volume to some of the largest rivers in Europe. It is evident, therefore, that when we are speculating on the excavating force which a river may have exerted in any particular valley, the most important question is not the volume of the existing stream, nor the present levels of its channel, nor even the nature of the rocks, but the probability of a succession of floods at some period since the time when the valley may have been first elevated above the sea. For several months after the debacle of 1818, the Dransa, having no settled channel, shifted its position continually from one side to the other of the valley, carrying away newly erected bridges, undermining houses, and continuing to be charged with as large a quantity of earthy matter as the fluid could hold in suspension. I visited this valley four times after the flood, and was witness to the sweeping away of a bridge and the undermining of part of a house. The greater part of the ice barrier was then standing, presenting vertical cliffs 150 feet high, like ravines in the lava currents of Edna or Overn, where they are intersected by rivers. Inundations, precisely similar, are recorded to have occurred at former periods in this district and from the same cause. In 1595, for example, a lake burst, and the waters descending with irresistible fury destroyed the town of Martini, where from 60 to 80 persons perished. In a similar flood 50 years before, 140 persons were drowned. End of chapter 14, part 2, The Principles of Geology, chapter 14, part 3. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, visit LibriVox.org. Principles of Geology by Charles Lyle. Flood at Tivoli, 1826. I shall conclude with one more example derived from a land of classic recollections. The ancient Tiber, and which, like all the other inundations above alluded to, occurred within the present century. The younger Pliny, it will be remembered, describes a flood on the Aeneo, which destroyed woods, rocks, and houses with the most sumptuous villas and works of art. For four or five centuries consecutively, this headlong stream, as Horace truly called it, has often remained within its bounds, and then, after so long an interval of rest, has at different periods inundated its banks again and widened its channel. The last of these catastrophes happened 15th of November, 1826, after heavy rains, such as produced the floods before alluded to in Scotland. The waters appear also to have been impeded by an artificial dike, by which they were separated into two parts, a short distance above Tivoli. They broke through this dike, and leaving the left trench dry, precipitated themselves with their whole weight on the right side. Here they undermined, in the course of a few hours, a high cliff, and widened the river's channel about 15 paces. On this height stood the Church of Saint Lucia, and about 36 houses of the town of Tivoli, which were all carried away, presenting as they sank into the roaring flood a terrific scene of destruction to the spectators on the opposite bank. As the foundations were gradually removed, each building, some of them edifices of considerable height, was first traversed with numerous rents, which soon widened into large fissures, until at length the roofs fell in with a crash, and then the walls sunk into the river and were hurled down the cataract below. The destroying agency of the flood came within 200 yards of the precipice on which the beautiful Temple of Vesta stands, but fortunately this precious relic of antiquity was spared, while the wreck of modern structures was hurled down the abyss. Vesta, it will be remembered in the heathen mythology, personified the stability of the earth, and when the Samian astronomer Aristarchus first taught that the earth revolved on its axis and round the sun, he was publicly accused of impiety, quote, for removing the everlasting Vesta from her place, end quote. Playfair observed that when Hutton ascribed instability to the earth's surface and represented the continents which we inhabit as the theater of incessant change and movement, his antagonists, who regarded them as unalterable, assailed him in a similar manner with accusations founded on religious prejudices. We might appeal to the excavating power of the Aeneo as corroborative of one of the most controversial parts of the Huttonian theory, and if the days of omens had not gone by, the geologists who now worshiped Vesta might regard the late catastrophe as portentous. We may at least recommend the modern votaries of the goddess to lose no time in making a pilgrimage to her shrine for the next flood may not respect the temple. Excavation of rocks by running water. The rapidity with which even the smallest streams hollow out deep channels in soft and destructible soils is remarkably exemplified in volcanic countries where the sand and half-consolidated tufts opposed by a slight resistance to the torrents which descend the mountainside. After the heavy rains which followed the eruption of Vesuvius in 1824, the water flowing from the Atrio de Cavallo cut in three days, a new chasm through strata of tough and ejected volcanic matter to the depth of 25 feet. I found the old mule road in 1828 intersected by this new ravine. The gradual erosion of deep chasms through some of the hardest rocks by the constant passage of running water charged with foreign matter is another phenomenon of which striking examples may be induced. Illustrations of this excavating power are presented by many valleys in central France where the channels of rivers have been barred up by solid currents of lava through which the streams have re-excavated a passage to the depth of from 20 to 70 feet and upwards and often of great width. In these cases there are decisive proofs that neither the sea nor any denuding wave or extraordinary body of water has passed over the spot since the melted lava was consolidated. Every hypothesis of the intervention of sudden and violent agency is entirely excluded because the cones of loose scoriae out of which the lavas flowed are oftentimes at no great elevation above the rivers and have remained undisturbed during the whole period which has been sufficient for the hollowing out of such enormous ravines. Recent excavation by the Cimetto but I shall at present combine myself to examples derived from events which have happened since the time of history. At the western base of Etna a current of lava figure 16 descending from near the summit of the great volcano has flowed to the distance of five or six miles and then reached the alluvial plain of the Cimetto the largest of the Sicilian rivers which skirts the base of Etna and falls into the sea a few miles south of Catania. The lava entered the river about three miles above the town of Adorno and not only occupied its channel for some distance but crossing to the opposite side of the valley accumulated there in a rocky mass. Gamalero gives the year 1603 as the date of the eruption. The appearance of the current clearly proves that it is one of the most modern of those of Etna for it has not been covered or crossed by subsequent streams or ejections and the olives which have been planted on its surface were all of small size when I examined the spot in 1828 yet they were older than the natural wood on the same lava. In the course therefore of about two centuries the Cimetto had eroded a passage from 50 to several hundred feet wide and in some parts from 40 to 50 feet deep. The portion of lava cut through is in no part porous or scoriacious but consists of a compact homogenous mass of hard blue rock somewhat inferior in weight to ordinary basalt and containing crystals of olivine and glassy felspar. The general declivity of this part of the bed of the Cimetto is not considerable but in consequence of the unequal waste of the lava two waterfalls occur at Passo Manzanelli each about six feet in height. Here the chasm the figure 16 is about 40 feet deep and only 50 broad. The sand and pebbles in the riverbed consist chiefly of a brown quartzose sandstone derived from the upper country but the materials of the volcanic rock itself must have greatly assisted the attrition. This river like the Calta Biano on the eastern side of Etna has not yet cut down to the ancient bed of which it was dispossessed and of which the probable position is indicated in the ennex diagram. See figure 16. On entering the narrow ravine where the water foams down the two cataracts we are entirely shut out from all view of the surrounding country and a geologist who is accustomed to associate the characteristic features of the landscape with the relative age of certain rocks can scarcely dissuade himself from the belief that he is contemplating a scene in some rocky gorge of a primary district. The external forms of the hard blue lava are as massive as any of the most ancient trap rocks of Scotland. The solid surface is in some parts smooth and almost polished by attrition and covered in others with a white lichen which imparts to it an air of extreme antiquity so as greatly to heighten the delusion. But the moment we re-ascend the cliff the spell is broken for we scarcely recede a few paces before the ravine and river disappear and we stand on the black and rugged surface of a vast current of lava which seems unbroken and which we can trace up nearly to the distant summit of that majestic cone which Pindar called the pillar of heaven and which still continues to send forth a fleecy wreath of vapor reminding us that its fires are not extinct and that it may again give out a rocky stream wherein other scenes like that now described may present themselves to future observers. Falls of Niagara The Falls of Niagara afford a magnificent example of the progressive excavation of a deep valley in solid rock. That river flows over a flat table land in a depression of which Lake Erie is situated where it issues from the lake it is clearly a mile in width and 330 feet above Lake Ontario which is about 30 miles distant. For the first 15 miles below Lake Erie the surrounding country comprising Upper Canada on the west and the state of New York on the east is almost on a level with its banks and nowhere more than 30 or 40 feet above them see figure 17. The river being occasionally interspersed with low wooded islands and having sometimes a width of three miles glides along at first with a clear smooth and tranquil current falling only 15 feet in as many miles and in this part of its course resembling an arm of Lake Erie but its character is afterwards entirely changed on approaching the rapids where it begins to rush and foam over a rocky and uneven limestone bottom for the space of nearly a mile to let length it is thrown down perpendicularly 160 feet at the falls here the river is divided into two sheets of water by an island the largest cataract being more than a third of a mile broad the smaller one having a breadth of 600 feet when the water has precipitated itself into an unfathomable pool it rushes with great velocity down the sloping bottom of a narrow chasm for a distance of seven miles this ravine varies from 200 to 400 yards in width from cliff to cliff contrasting therefore strongly in its breadth with that of the river above its depth is from 200 to 300 feet and it intersects for about seven miles the table land before described which terminates suddenly at Queenstown in an escarpment or long line of inland cliff facing northwards toward Lake Ontario the Niagara on reaching the escarpment and issuing from the gorge enters the flat country which is so nearly on a level with Lake Ontario that there is only a fall of about four feet in the seven additional miles which intervene between Queenstown and the shores of that lake it has long been the popular belief that the Niagara once flowed in a shallow valley across the whole platform from the present side of the falls to the escarpment called the Queenstown Heights where it is supposed that the cataract was first situated and that the river has been slowly eating its way backwards through the rocks for the distance of seven miles this hypothesis naturally suggests itself to every observer who sees the narrowness of the gorge at its termination and throughout its whole course as far up as the falls above which point the river expands as before stated the boundary cliffs of the ravine are usually perpendicular and in many places undermined on one side by the impetuous stream the uppermost rock of the table land at the falls consists of hard limestone a member of the Silurian series about 90 feet thick beneath which lie soft shales of equal thickness continually undermined by the action of the spray which rises from the pool into which so large a body of water is projected and is driven violently by gusts of wind against the base of the precipice in consequence of this action and that of frost the shale disintegrates and crumbles away and portions of the incumbent rock overhang 40 feet and often when unsupported tumble down so that the falls do not remain absolutely stationary at the same spot even for half a century accounts have come down to us from the earliest period of observation of the frequent destruction of these rocks and the sudden descent of huge fragments in 1818 and 1828 are said to have shaken the adjacent country like an earthquake the earliest travelers Hennepin and Kalm who in 1678 and 1751 visited the falls and published views of them attest the fact that the rocks have been suffering from dilapidation for more than a century and a half and that some slight changes even in the scenery of the cataract have been brought about within that time the idea therefore of perpetual and progressive waste is constantly present to the mind of every beholder and as that part of the chasm which has been the work of the last 150 years resembles precisely in depth width and character the rest of the gorge which extends seven miles below it is most natural to infer that the entire ravine has been hollowed out in the same manner by the recession of the cataract it must at least be conceded that the river supplies an adequate cause for executing the whole task thus assigned to it providing we grant sufficient time for its completion as this part of the country was a wilderness till near the end of the last century we can obtain no accurate data for estimating the exact rate at which the cataract has been receding mr bakewell son of the eminent geologist of that name who visited the niagara in 1829 made the first attempt to calculate from the observations of one who had lived 40 years at the falls and who had been the first settler there that the cataract had during that period gone back about a yard annually but after the most careful inquiries which i was able to make during my visit to the spot in 1841 to 2 i came to the conclusion that the average of one foot a year would be a much more probable conjecture in that case it would have required 35 000 years for the retreat of the falls from the escarpment of queenstown to their present site it seems by no means improbable that such a result would be no exaggeration of the truth although we cannot assume that the retrograde movement has been uniform an examination of the geological structure of the district as laid open in the ravine shows that at every step in the process of excavation the height of the precipice the hardness of the materials at its base and the quantity of fallen matter to be removed must have varied at some points it may have receded much faster than at present but in general its progress was probably slower because the cataract when it began to recede must have had nearly twice its present height from observations made by me in 1841 when i had the advantage of being accompanied by mr. hall state geologist of new york and in 1842 when i reexamined the niagara district i obtained geological evidence of the former existence of an old riverbed which i have no doubt indicates the original channel through which the waters once flowed from the falls to queenstown at the height of nearly 300 feet above the bottom of the present gorge the geological monuments alluded to consist of patches of sand and gravel 40 feet thick containing fluviatile shells of the genera unio cyclus millennia etc such as now inhabit the waters of the niagara above the falls the identity of the fossil species with the recent is unquestionable and these freshwater deposits occur at the edge of the cliffs bounding the ravine so that they prove the former extension of an elevated shallow valley four miles below the falls a distinct prolongation of that now occupied by the niagara in the elevated region intervening between lake eerie and the falls whatever theory be framed for the hollowing out of the ravine further down or for the three miles which intervene between the whirlpool and queenstown it will always be necessary to suppose the former existence of a barrier of rock not of loose and destructive materials such as those composing the drift in this district somewhere immediately below the whirlpool by that barrier the waters were held back for ages when the fluviatile deposit 40 feet in thickness and 250 feet above the present channel of the river originated if we are led by this evidence to admit that the cataract has cut back its way for four miles we can have little hesitation in referring the excavation of the remaining three miles below to a like agency the shape of the chasm being precisely similar there have been many speculations respecting the future recession of the falls and the deluge that might be occasioned by the sudden escape of the waters of lake eerie if the ravine should ever be prolonged 16 miles backwards but a more accurate knowledge of the geological succession of the rocks brought to light by the state survey has satisfied every geologist that the falls would diminish gradually in height before they traveled back two miles and in consequence of a gentle dip of the strata to the south the massive limestone now at the top would then be at their base and would retard and perhaps put an effectual stop to the excavating process end of chapter 14 part 3 chapter 15 part 1 of principles of geology this is a liverbox recording all liverbox recordings are in the public domain for more information or to volunteer please visit liverbox.org principles of geology by charles liel chapter 15 transportation of solid matter by ice carrying power of river ice rocks annually conveyed into the saint lorence by its tributaries ground ice its origin and transporting power glaciers theory of their downward movement smoothed and grooved rocks the moraine unstratified icebergs covered with mud and stones limits of glaciers and icebergs their effects on the bottom when they run a ground packing of coast ice boulders drifted by ice on the coast of labrador and blocks moved by ice in the Baltic the power of running water to carry sand gravel and fragments of rock to considerable distances is greatly augmented in those regions where during some part of the year the frost is of sufficient intensity to convert the water either at the surface or bottom of rivers into ice this subject may be considered under three different heads first the effect of surface ice and ground ice and enabling streams to remove gravel and stones to a distance secondly the action of glaciers in the transport of boulders and in the polishing and scratching of rocks thirdly the floating off of glaciers charged with solid matter into the sea and the drifting of icebergs and coast ice river ice pebbles and small pieces of rock may be seen entangled in ice and floating annually down the Tay in Scotland as far as the mouth of that river similar observations might doubtless be made respecting almost all the larger rivers of England and Scotland but there seems reason to suspect that the principal transfer from place to place of pebbles and stones adhering to ice goes on unseen by us underwater for although the specific gravity of the compound mass may cause it to sink it may still be very buoyant and easily borne along by a feeble current the ice moreover melts very slowly at the bottom of running streams in winter as the water there is often nearly at the freezing point as will be seen from what will be said in the sequel of ground ice as we traverse Europe in the latitudes of Great Britain we find the winters more severe and the rivers more regularly frozen over emla river relates that being at Memmel in the Baltic in 1821 when the ice of the river Neiman broke up he saw a mass of ice 30 feet long which had descended the stream and had been thrown ashore in the middle of it was a triangular piece of granite about a yard in diameter resembling in composition the red granite of Finland when rivers in the northern hemisphere flow from south to north the ice first breaks up in the higher part of their course and the flooded waters bearing along large icy fragments often arrive at parts of the stream which are still firmly frozen over great inundations are thus frequently occasioned by the obstructions thrown in the way of the descending waters as in the case of the Mackenzie in North America and the Ertisch, Obie, Yannissi, Lena and other rivers of Siberia a partial stoppage of this kind lately occurred on January 31st of 1840 in the Vistula about a mile and a half above the city of Danzig where the river choked up by packed ice was made to take a new course over its right bank so that it hollowed out in a few days a deep and broad channel many leagues in length through a tract of sandhills which were from 40 to 60 feet high in Canada where the winter's cold is intense in a latitude corresponding to that of central France several tributaries of the St. Lawrence begin to thaw in their upper course while they remain frozen over lower down and thus large slabs of ice are set free and thrown upon the unbreaking sheet of ice below then begins what is called the packing of the drifted fragments that is to say one slab is made to slide over another until a vast pile is built up and the whole thing being frozen together is urged onwards by the force of the dammed up waters and drift ice thus propelled it not only forces along boulders but breaks off from cliffs which border the rivers huge pieces of projecting rock by this means several buttresses of solid masonry which up to the year 1836 supported a wooden bridge on the St. Maurice which falls into the St. Lawrence near the town of the Tree Riviera latitude 46 degrees 20 minutes were thrown down and conveyed by the ice into the main river and instances have occurred at Montreal of wharfs and stone buildings from 30 to 50 feet square having been removed in a similar manner we learn from captain Bayfield that anchors laid down within high watermark to secure vessels hauled on shore for the winter must be cut out of the ice on the approach of spring or they would be carried away in 1834 the Glenairs bower anchor weighing half a ton was transported some yards by the ice and so firmly was it fixed that the force of the moving ice broke a chain cable suited for a 10 gun brig and which had rode the Glenair during the heaviest gales in the gulf had not this anchor been cut out of the ice it would have been earned into deep water and lost the scene represented in the annexed plate from a drawing by Lieutenant Bowen R.N. will enable the reader to comprehend the incessant changes which the transport of boulders produces annually on the low islands shores and bed of the St. Lawrence above Quebec the fundamental rocks at Richelieu rapid situated in latitude 46 degrees north are limestone and slate which are seen at low water to be covered with boulders of granite these boulders owe their spheroidal form chiefly to weathering or action of frost which causes the surface to exfoliate and concentric plates so that all the more prominent angles are removed at the point a is a cavity in the mud or sand of the beach now filled with water which was occupied during the preceding winter of 1835 by the huge erratic B a mass of granite 70 tons weight found in the spring following 1836 at a distance of several feet from its former position many small islands are seen on the river such as C and D which affords still more striking proofs of the carrying and propelling power of ice these islets are never underwater yet every winter ice is thrown upon them in such abundance that it packs to the height of 20 and even 30 feet bringing with it a continual supply of large stones or boulders and carrying away others the greatest number being deposited according to lieutenant bowen on the edge of deep water on the island D on the left of the accompanying view a lighthouse is represented consisting of a square wooden building which having no other foundation than the boulders requires to be taken down every winter and rebuilt on the reopening of the river these effects of frost which are so striking on the st. Lawrence above Quebec are by no means displayed on a smaller scale below that city where the gulf rises and falls with the tide on the contrary it is the estuary between the latitudes of 47 and 49 degrees that the greatest quantity of gravel and boulders of large dimensions are carried down annually towards the sea here the frost is so intense that a dense sheet of ice is formed at low water which on the rise of the tide is lifted up broken and thrown in heaps on the extensive shoals which border the estuary when the tide recedes this packed ice is exposed to a temperature sometimes 30 degrees below zero which freezes together all the loose pieces of ice as well as the granite and other boulders the whole of these are often swept away by a high tide or when the river is swollen by the melting of the snow in spring one huge block of granite 15 feet long by 10 feet both in width and height and estimated to contain 1500 cubic feet was conveyed in this manner to some distance in the year 1837 its previous position being well known as up to that time it had been used by captain bayfield as a mark for the surveying station ground ice when a current of cold air passes over the surface of a lake or stream it abstracts from it a quantity of heat and the specific gravity of the water being thereby increased the cooled portion sinks this circulation may continue until the whole body of fluid has been cooled down to the temperature of 40 degrees fahrenheit after which if the cold increase the vertical movement ceases the water which is uppermost expands and floats over the heavier fluid below and when it has attained a temperature of 32 degrees fahrenheit it sets into a sheet of ice it should seem therefore impossible according to this law of conglulation that I should ever form at the bottom of a river and yet such is the fact and many speculations have been hazard to account for so singular a phenomenon and ergo is of opinion that the mechanical action of a running stream produces a circulation by which the entire body of water is mixed up together and cooled alike and the whole being thus reduced to the freezing point ice begins to form at the bottom for two reasons first because there is less motion there and secondly because the water is in contact with solid rock or pebbles which have a cold surface whatever explanation we adopt there is no doubt of the fact that in countries where the intensity and duration of cold is great rivers and torrents acquire an increase of carrying power by the formation of what is called ground ice even in the tames we learn from dr plot that pieces of this kind of ice having gravel frozen on their underside rise up from the bottom in winter and float on the surface in the Siberian rivers the whites describes large stones as having been brought up from the river's bed in the same manner and made to float glaciers in the temperate zone the snow lies for months in winter on the summit of every high mountain while in the arctic regions a long summer's day of half a year's duration is insufficient to melt the snow even on land just raised above the level of the sea it is therefore not surprising since the atmosphere becomes colder in proportion as we ascend in it that there should be heights even in tropical countries where the snow never melts the lowest limit to which the perpetual snow extends downwards from the tops of mountains at the equator is an elevation of not less than 16 000 feet above sea while in the swiss alps in latitude 46 degree north it reaches as low as 8500 feet above the same level the loftier peaks of the alpine chain being from 12 to 15 000 feet high the frozen mass augmenting from year to year would add indefinitely to the altitude of alpine summits were it not relieved by its descent through the larger and deeper valleys to regions far below the general snow line to these it slowly finds its way in the form of rivers of ice called glaciers the consolidation of which is produced by pressure and by the conglolation of water infiltrated into the porous mass which is always undergoing partial liquefaction and receiving in summer occasional showers of rain on its surface in a day of hot sunshine or mild rain innumerable rills of pure and sparkling water run in icy channels along the surface of the glaciers which in the night shrink and come to nothing they are often precipitated in bold cascades into deep fissures in the ice and contribute together with springs to form torrents which flow in tunnels at the bottom of the glaciers for many a league and at length issue at their extremities from beneath beautiful caverns or arches the waters of these streams are always densely charged with the finest mud produced by the grinding of rock and sand under the weight of the moving mass the length of the swiss glaciers is sometimes 20 miles their width in the middle portion where they are broadest occasionally two or three miles their depth or thickness sometimes more than 600 feet when they descend steep slopes and precipices or are forced through narrow gorges the ice is broken up and assumes the most fantastic and picturesque forms with lofty peaks and pinnacles projecting above the general level these snow-white masses are often relieved by a dark background of pines as in the valley of the Chamonix and are not only surrounded with abundance of the wild rhododendron in full flower but encroach still lower into the region of cultivation and trespass on fields where the tobacco plant is flourishing by the side of the peasants hut the cause of glacier motion has of late been a subject of careful investigation and much keen controversy although a question of physics rather than of geology it is too interesting to allow me to pass it by without some brief mention desa sure whose travels in the alps are full of original observations as well as sound and comprehensive general views conceive that the weight of the ice might be sufficient to urge it down the slope of the valley if the sliding motion were aided by the water flowing at the bottom for this gravitation theory chèpentier followed by augusts substituted the hypothesis of dilation the most solid ice is always permeable to water and penetrated by innumerable fissures and capillary tubes often extremely minute these tubes imbibe the aqueous fluid during the day which freezes it is said in the cold of the night and expands in the act of congliation the distension of the whole mass exerts an immense force tending to propel the glacier in the direction of least resistance in other words down the valley this theory was opposed by mr hopkins on mathematical and mechanical grounds in several able papers among other objections he pointed out that the friction of so enormous a body is a glacier on its bed is so great that the vertical direction would always be that of least resistance and if a considerable distension of the mass should take place by the action of freezing it would tend to increase its thickness rather than accelerate its downward progress he also contended and his arguments were illustrated by many ingenious experiments that a glacier can move along an extremely slight slope solely by the influence of gravitation owing to the constant dissolution of ice in contact with the rocky bottom and the number of separate fragments into which the glacier is divided by fissures so that freedom of motion is imparted to its several parts somewhat resembling that of an imperfect fluid to this view professor james forbes objected that gravitation would not supply an adequate cause for the sliding of solid ice down slopes having an inclination of no more than four or five degrees still less would it explain how the glacier advances where the channel expands and contracts the murdi glace and shamoni for example after being two thousand yards wide passes through a straight only 900 yards in width such a gorge it is contended would be choked up by the advance of any solid mass even if it be broken up into numerous fragments the same acute observer remarked that that water in the fissures and pores of glaciers cannot and does not part with its latent heat so as to freeze every night to a great depth or far in the interior of the mass had the dilation theory been true the chief motion of the glacier would have occurred about sunset when the freezing of the water must be greatest and it had in fact been first assumed by those who favored that hypothesis that the mass moved faster at the sides where the melting of the ice was promoted by the sun's heat reflected from boundary precipices august seas appears to have been the first to commence in 1841 aided by a skillful engineer M. Escher de la lint a series of exact measurements to ascertain the laws of glacier motion and he soon discovered contrary to his preconceived notions that the stream of ice is moved more slowly at the sides than at the center and faster in the middle region of the glacier than at its extremity professor james fours who had joined mr august seas during his earlier investigations in the alps undertook himself an independent series of experiments which he followed up with great perseverance to determine the laws of glacier motion these he found to agree very closely with the laws governing the course of rivers their progress being greater in the center than at the sides and more rapid at the surface than at the bottom this fact was verified by carefully fixing a great number of marks in the ice arranged in a straight line which gradually assumed a beautiful curve the middle part pointing down the glacier and showing a velocity there double or treble that of the lateral parts he ascertained that the rate of advance by night was nearly the same as by day and that even the hourly march of the icy stream could be detected although the progress might not amount to more than six or seven inches in 12 hours by the incessant though invisible advance of the marks placed on the ice time says mr forbes was marked out as by a shadow on a dial and the unequivocal evidence which i obtained that even while walking on a glacier we are day by day and hour by hour imperceptibly carried on by the resistless flow of the icy stream filled me with admiration in order to explain this remarkable regularity of motion and its obedience to laws so strictly analogous to those of fluids the same writer proposed the theory that the ice instead of being solid and compact is a viscous or plastic body capable of yielding to great pressure and the more so in proportion as its temperature is highest and as it approaches more nearly to the melting point he endeavors to show that this hypothesis will account for many complicated phenomena especially for a ribboned or vane structure which is everywhere observable in the ice and might be produced by lines of discontinuity arising from the different rates at which the various portions of the semi-rigid glacier advance and pass each other many examples are reduced to prove that a glacier can model itself to the form of the ground over which it is forced exactly as would happen if it possessed a certain duosility and this power of yielding under intense pressure is shown not to be irreconcilable with the idea of the ice being sufficiently compact to break it into fragments when the strain upon its parts is excessive as where the glacier turns a sharp angle or descends upon a rapid or convex slope the increased velocity in summer is attributed partly to the greater plasticity of the ice when not exposed to intense cold and partly to the hydrostatic pressure of the water in the capillary tubes which imbibe more of this liquid in the hot season on the assumption of the ice being a rigid mass mr. hopkins attributed the more rapid motions in the center to the unequal rate at which the broad stripes of ice intervening between longitudinal fissures advance but besides that there are parts of the glacier where no such fissures exist such a mode of progression says mr. Forbes would cause the borders of large transverse rents or crevices to be jagged like a saw instead of being perfectly even and straight edged an experiment recently made by mr. christie secretary to the royal society appears to demonstrate that ice under great pressure possesses a sufficient degree of molding and self-adapting power to allow it to be acted upon as if it were a pasty substance a hollow shell of iron an inch and a half thick the interior being 10 inches in diameter was filled with water in the course of a severe winter and exposed to the frost with the fuse hole uppermost a portion of the water expanded in freezing so as to protrude a cylinder of ice from the fuse hole and this cylinder continued to grow inch by inch in proportion as the central nucleus of water froze as we cannot doubt that an outer shell of ice is first formed and then another within the continued rise of the column through the fuse hole must proceed from the squeezing of successive shells of ice concentrically formed through the narrow orifice and yet the protruded cylinder consisted of entire and not fragmentary ice end of chapter 15 part 1 chapter 15 part 2 of principles of geology this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org principles of geology by Charles Lyell chapter 15 part 2 the agency of glaciers and producing permanent geological changes consists partly in their power of transporting gravel sand and huge stones to great distances and partly in the smoothing polishing and scoring of their rocky channels and the boundary walls of the valleys through which they pass at the foot of every steep cliff or precipice in high alpine regions a talus is seen of rocky fragments detached by the alternate action of frost and thaw if these loose masses instead of accumulating on a stationary base happen to fall upon a glacier they will move along with it and in place of a single heap they will form in the course of years a long stream of blocks if a glacier be 20 miles long in its annual progression about 500 feet it will require about two centuries for a block thus lodged upon its surface to travel down from the higher to the lower regions or to the extremity of icy mass this terminal point remains usually unchanged from year to year although every part of the ice is in motion because the liquefaction by heat is just sufficient to balance the onward movement of the glacier which may be compared to an endless file of soldiers pouring into a breach and shot down as fast as they advance the stones carried along on the ice are called in Switzerland the moraines of the glacier there is always one line of blocks on each side or edge of the icy stream and often several in the middle where they are arranged in long ridges or mounds often several yards high the cause of these medial moraines was first explained by augustsies who referred them to the confluence of tributary glaciers upon the union of two streams of ice the right lateral moraine of one of the streams comes in contact with the left lateral moraine of the other and they afterwards move on together in the center if the confluent glaciers are equal in size or nearer to one side if unequal all sand and fragments of soft stone which fall through fissures and reach the bottom of the glaciers or which are interposed between the glacier and the steep sides of the valley are pushed along and ground down into mud while the larger and harder fragments have their angles worn off at the same time the fundamental and boundary rocks are smoothed and polished and often scored with parallel furrows or with lines and scratches produced by hard minerals such as crystals of quartz which act like diamond upon glass this effect is perfectly different from that caused by the action of water or a muddy torrent forcing along heavy fragments for when stones are fixed firmly in the ice and pushed along by it under great pressure in straight lines they scoop out long rectilinear furrows or grooves parallel to each other the discovery of such markings at various heights far above the surface of the existing glaciers and for miles beyond their present terminations affords geological evidence of the former extension of the ice beyond its present limits in switzerland and other countries the moraine of the glacier observed chef entier is entirely devoid of stratification for there has been no sorting of the materials as in the case of sand mud and pebbles when deposited by running water the ice transports indifferently and to the same spots the heaviest blocks and the finest particles mingling all together and leaving them in one confused and promiscuous heap wherever it melts icebergs in countries situated in high northern latitudes like spitsbergen between 70 and 80 degrees north glaciers loaded with mud and rock descend to the sea and their huge fragments of them float off and become icebergs scores be counted 500 of these bergs drifting along in latitudes of 69 and 70 degrees north which rose above the surface from the height of one to 200 feet and measured from a few yards to a mile in circumference many of them were loaded with beds of earth and rock of such thickness that the weight was conjectured to be from 50 000 to 100 000 tons specimens of the rocks were obtained and among them were granite mycoshists clayslate granular felspar and greenstone such bergs must be of great magnitude because the mass of ice below the level of the water is about eight times greater than of above wherever they are dissolved it is evident that the moraine will fall to the bottom of the sea in this manner may submarine valleys mountains and platforms become strewed over with gravel sand mud and scattered blocks of foreign rock of a nature perfectly dissimilar from all in the vicinity and which may have been transported across unfathomable abysses if the bergs happen to melt and still water so that the earthy and stony materials may fall tranquilly to the bottom the deposit will probably be unstratified like the terminal moraine of a glacier but whatever the materials are under the influence of a current of water as they fall they will be sorted and arranged according to their relative weight and size and therefore more or less perfectly stratified in a former chapter it was stated that some ice islands have been known to drift from baffins bay to the azores and from the south pole to the immediate neighborhood of the cape of good hope so that the area over which the effects of moving ice may be experienced comprehends a large portion of the globe we learn from van voek that the most southern point on the continent of europe at which a glacier comes down to the sea is in norwayed in latitudes 67 degrees north but mr darwin has shown that they extend to the sea in south america and latitudes more than 20 degrees nearer to the equator than in europe as for example in chile where in the gulf of penas latitude 46 degrees 40 minutes south or in the latitude of central france and in sir george eerie's sound and the latitude of ferris they give origin to icebergs which were seen in 1834 carrying angular pieces of granite and stranding them in fjords where the shores were composed of clay slate a large proportion however of the ice island scene floating both in the northern and southern hemispheres are probably not generated by glaciers but rather by the accumulation of coast ice when the sea freezes at the base of a lofty precipice the sheet of ice is prevented from adhering to the land by the rise and fall of the tide nevertheless it often continues onto the shore at the foot of the cliff and receives ascensions of drift snow blown from the land under the weight of the snow the ice sinks slowly if the water be deep and the snow is gradually converted into ice by partial liquefaction and recongilation in this manner islands of ice of great thickness and many leagues in length originate and are eventually blown out to sea by offshore winds and their interior are enclosed many fragments of stone which had fallen upon them from overhanging cliffs during their formation such floating icebergs are commonly flat topped but their lower portions are liable to melt in latitudes where the ocean at a moderate depth is usually warmer than the surface water and the air hence their center of gravity changes continually and they turn over and assume very irregular shapes in a voyage of discovery made in the Antarctic regions in 1839 a dark colored angular mass of rock was seen embedded in an iceberg drifting along in mid ocean in latitude 61 degrees south that part of the rock which was visible was about 12 feet in height and from five to six in width but the dark color of the surrounding ice indicated that it much more of the stone was concealed a sketch made by mr. McNabb when the vessel was within a quarter of a mile of it is now published this iceberg one of many observed at sea on the same day was between 250 and 300 feet high and was no less than 1400 miles from any certainly known land it is exceedingly improbable says mr. Darwin in his notice of the phenomenon that any land will hereafter be discovered within a hundred miles of this spot and it must be remembered that the erratic was still firmly fixed in the ice and may have sailed for many a league farther before it dropped to the bottom captain sir james ross in his Antarctic voyage in 1841 42 and 43 saw multitudes of icebergs transporting stones and rocks of various sizes with frozen mud in high southern latitudes his companion dr. j hooker informs me that he came to the conclusion that most of the southern icebergs have stones in them although they are usually concealed from view by the quantity of snow which falls upon them in the account given by mr's decent simpson of their recent arctic discoveries we learned that in latitude 71 degrees north longitude 156 degrees west they found a long low spit named point barrow composed of gravel and coarse sand in some parts more than a quarter of a mile broad which the pressure of the ice had forced up into numerous mounds that viewed from a distance assumed the appearance of huge boulder rocks this fact is important as showing how masses of drift ice winds stranding on submarine banks may exert a lateral pressure capable of bending and dislocating any yielding strata of gravel sand or mud the banks on which icebergs occasionally run aground between baffins bay and newfoundland are many hundred feet underwater and the force with which they are struck will depend not so much on the velocity as the momentum of the floating ice islands the same burg is often carried away by a change of wind and then driven back again upon the same bank or it is made to rise and fall by the waves of the ocean show that it may alternately strike the bottom with its whole weight and then be lifted up again until it has deranged the superficial beds over a wide area in this manner the geologists may account perhaps for the circumstance that in scandinavia scotland and other countries where erratics are met with the beds of sand a loam and gravel are often vertical bent and contorted into the most complicated folds while the underlying strata although composed of equally pliant materials are horizontal but some of these curvatures of loose strata may also have been due to repeated alternations of layers of gravel and sand ice and snow the melting of the latter having caused the intercalated beds of indestructible matter to assume their present anomalous position there can be little doubt that icebergs must often break off the peaks and projecting points of submarine mountains and must grate upon and polish their surface furrowing or scratching them in precisely the same way as we have seen that glaciers act on the solid rocks over which they are propelled to conclude it appears that large stones mud and gravel are carried down by the ice of rivers estuaries and glaciers into the sea where the tides and currents of the ocean aided by the wind cause them to drift for hundreds of miles from the place of their origin although it will belong more properly to the seventh and eighth chapters to treat of the transportation of solid matter by the movements of the ocean i shall adhere what i have farther to say on this subject in connection with ice the saline matter which seawaters hold in solution prevents its congliation except where the most intense cold prevails but the drifting of the snow from the land often renders the surface water brackish near the coast so that a sheet of ice is readily formed there and by this means a large quantity of gravel is frequently conveyed from place to place and heavy boulders also when the coast ice is packed into dense masses both the large and small stones thus conveyed usually travel in one direction like shingle beaches and this was observed to take place on the coast of labrador and gulf of st laurence between the latitudes 50 and 60 degrees north by captain bayfield during his late survey the line of coast alluded to is strewed over for a distance of 700 miles with ice-born boulders often six feet in diameter which are for the most part on their way from north to south or in the direction of the prevailing current some points on this coast have been observed to be occasionally deserted and then again at another season thickly bestrewed with erratics the accompanying drawing for which i am indebted to lieutenant bowen rn represents the ordinary appearance of the labrador coast between the latitudes of 50 degrees and 60 degrees north countless blocks chiefly granatic and of various sizes are seen lying between high and low watermark captain bayfield saw similar masses carried by ice through the straits of bell isle between newfoundland and the american continent which he conceives may have traveled in the course of years from baffin's bay a distance which may be compared in our hemisphere to the drifting of erratics from lapland and iceland as far south as germany france and england it may be asked in what manner have these blocks been originally detached we may answer that some have fallen from precipitous cliffs others have been lifted up from the bottom of the sea adhering by their tops to the ice while others may have been brought down by rivers and glaciers the erratics of north america are sometimes angular but most of them have been rounded either by friction or decomposition the granite of canada as before remarked has a tendency to concentric exfoliation and scales off in spheroidal coats when exposed to the spray of the sea during severe frosts the range of the thermometer in that country usually exceeds in the course of a year 100 degrees and sometimes 120 degrees Fahrenheit and to prevent the granite used in the buildings of quabac from peeling off in winter it is necessary to oil and paint the squared stones in parts of the Baltic such as the gulf of botnia where the quantity of salt in the water amounts in general to one fourth only that in the ocean the entire surface freezes over in winter to the depth of five or six feet stones are thus frozen in and afterwards lifted up about three feet perpendicularly to the melting of the snow in summer and then carried by floating ice islands to great distances professor von baer states in a communication on this subject to the academy of st petersburg that a block of granite weighing a million of pounds was carried by ice during the winter of 1837 to 38 from finland to the island of hockland and two other huge blocks were transported about the years 1806 and 1814 by packed ice on the south coast of finland according to the testimony of the pilots and inhabitants one block having traveled about a quarter of a mile and lying about 18 feet above the level of the sea more recently dr. forecomer has shown that in the sound the great belt and other places near the entrance of the Baltic ground ice forms plentifully at the bottom and then rises to the surface charged with sand and gravel stones and seaweed sheets of ice also with included boulders are driven up on the coast during storms and packed to a height of 50 feet to the motion of such masses but still more to that of the ground ice the danish professor attributes the striation of rocky surfaces forming the shores in bed of the sea and he relates a striking fact to prove that large quantities of rocky fragments are annually carried by ice out of the Baltic in the year 1807 he says at the time of the bombardment of the danish fleet an english loop of war riding at anchor in the roads of Copenhagen blew up in 1844 or 37 years afterwards one of our divers known to be a trustworthy man went down to save whatever might yet remain in the shipwrecked vessel he found the space between the decks entire but covered with blocks from six to eight cubic feet in size and some of them heaped one upon the other he also affirmed that all of the sung ships which he had visited in the sound were in like a manner strewed over with blocks dr. forkhammer also informs us that during an intense frost in february 1844 the sound was suddenly frozen over and sheets of ice driven by a storm were heaped up at the bottom of the bay of tarbejki threatening to destroy a fishing village on the shore the hole was soon frozen together into one mass and forced up on the beach forming a mound more than 16 feet high which threw down the walls of several buildings when i visited the spot the next day i saw ridges of ice the sand and pebbles not only on the shore but extending far out into the bottom of the sea showing how greatly its bed had been changed and how easily where it is composed of rock it may be furrowed and streaked by stones firmly fixed in the moving ice end of chapter 15 part 2 section 34 of principles of geology this is a libravox recording a libravox recordings are in the public domain for more information or to volunteer please visit libravox.org recording by dion jines subtlake city utah principles of geology by charles lile chapter 16 part one phenomena of springs origin of springs artesian wells borings at paris distinct causes by which mineral and thermal waters may be raised to the surface their connection with volcanic agency calciarius springs travertin of the elsa baths of san vinyan and of san filipo near rodicofani spheroidal structure in travertin lake of the sulfatara near rome travertin at cascade of tavoli gypsias salacious and ferrogenous springs brine springs carbonated springs disintegration of granite and avern petroleum springs pitch lake of trinidad origin of springs the action of running water on the surface of the land having been considered we may next turn our attention to what may be termed the subterranean drainage or the phenomena of springs everyone is familiar with the fact that certain porous soils such as loose sand and gravel absorb water with rapidity and that the ground composed of them soon dries up after heavy showers if a well be sunk in such soils we often penetrate to considerable depths before we meet with water but this is usually found on our approaching the lower parts of the formation where it rests on some impervious bed for here the water unable to make its way downwards in a direct line accumulates as in a reservoir and is ready to ooze out into any opening which may be made in the same manner as we see the salt water flow into and fill any hollow which we dig in the sands of the shore at low tide the facility with which water can percolate loose and gravelly soils is clearly illustrated by the effect of the tides in the tames between richmond and london the river in this part of its course flows through a bed of gravel overlying clay and the porous super stratum is alternately saturated by the water of the tames as the tide rises and then drained again to the distance of several hundred feet from the banks when the tide falls so that the wells in this tract regularly ebb and flow if the transmission of water through a porous medium be so rapid we cannot be surprised that springs should be thrown out on the side of a hill where the upper set of strata consist of chalk sand or other permeable substances while the subjacent are composed of clay or other retentive soils the only difficulty indeed is to explain why the water does not ooze out everywhere along the line of junction of the two formations as to form one continuous landsoak instead of a few springs only and these far distant from each other the principal cause of this concentration of the waters at a few points is first the frequency of rents and fissures which act as natural drains secondly the existence of inequalities in the upper surface of the impermeable stratum which lead the water as valleys do on the external surface of a country into certain low levels and channels that the generality of springs owe their supply to the atmosphere is evident from this that they become languid or entirely cease to flow after long droughts and are again replenished after a continuance of rain many of them are probably indebted for the constancy and uniformity of their volume to the great extent of the subterranean reservoirs with which they communicate and the time required for these to empty themselves by percolation such a gradual and regulated discharge is exhibited though in a less perfect degree in every great lake which is not sensibly affected in its level by sudden showers but only slightly raised so that its channel of efflux instead of being swollen suddenly like the bed of a torrent is enabled to carry off the surplus water gradually much light has been thrown of late years on the theory of springs by the boring of what are called by the French artesian wells because the method has long been known and practiced in Artois and it is now demonstrated that there are sheets and in some places currents of fresh water at various depths in the earth the instrument employed in excavating these wells is a large auger and the cavity board is usually from three to four inches in diameter if a hard rock is met with it is first triterated by an iron rod and the materials being thus reduced to small fragments or powder are readily extracted to hinder the sides of the well from falling in as also to prevent the spreading of the ascending water in the surrounding soil a jointed pipe is introduced formed of wood in Artois but in other countries more commonly of metal it frequently happens that after passing through hundreds of feet of retentive soils a water bearing stratum is at length pierced when the fluid immediately ascends to the surface and flows over the first rush of the water up the tube is often violent so that for a time the water plays like a fountain and then sinking continues to flow over tranquilly or sometimes remain stationary at a certain depth below the orifice of the well this spouting of the water in the first instance is probably owing to the disengagement of air and carbonic acid gas for both of these have been seen to bubble up with the water at sheerness at the mouth of the tames a well was bored on a low tongue of land near the sea through 300 feet of the blue clay of london below which a bed of sand and pebbles was entered belonging doubtless to the plastic clay formation when this stratum was pierced the water burst up with impetuosity and filled the well by another perforation at the same place the water was found at the depth of 328 feet below the surface clay it first rose rapidly to the height of 189 feet and then in the course of a few hours ascended to an elevation of eight feet above the level of the ground in 1824 a well was dug at fulham near the tames at the bishop of london's to the depth of 317 feet which after traversing the tertiary strata was continued through 67 feet of chalk the water immediately rose to the surface and the discharge was about 50 gallons per minute in the garden of the horticultural society at chiswick the borings passed through 19 feet of gravel 242 and a half feet of clay and loam and 67 and a half feet of chalk and the water then rose to the surface from a depth of 329 feet at the duke of northumberlands above chiswick the borings were carried to the extraordinary depth of 620 feet so as to enter the chalk when a considerable volume of water was obtained which rose four feet above the surface of the ground in a well of mr brooks at hammer smith the rush of water from a depth of 360 feet was so great as to inundate several buildings and do considerable damage and at tooting a sufficient stream was obtained to turn a wheel and raise the water to the upper stories of the houses in 1838 the total supply obtained from the chalk near london was estimated at six million gallons a day and in 1851 at nearly double that amount the increase being accompanied by an average fall of no less than two feet a year in the level to which the water rose the water stood commonly in 1822 at high water mark and had sunk in 1851 to 45 and in some wells to 65 feet below high water mark this fact shows the limited capacity of the subterranean reservoir in the last of three wells bored through the chalk at tours to the depth of several hundred feet the water rose 32 feet above the level of the soil and the discharge amounted to 300 cubic yards of water every 24 hours by way of experiment the sinking of a well was commenced at paris in 1834 which had reached in november 1839 a depth of more than 1600 english feet and yet no water ascended to the surface the government were persuaded by mesur or rago to persevere if necessary to the depth of more than 2000 feet but when they had descended above 1800 english feet below the surface the water rose through the tube which was about 10 inches in diameter so as to discharge half a million of gallons of limpid water every 24 hours the temperature of the water increased at the rate of 1.8 degrees fahrenheit for every 101 english feet as they went down the result agreeing very closely with the anticipations of the scientific advisors of this most spirited undertaking mr briggs the british consul in egypt obtained water between kyro and suez in a calcarius sand at the depth of 30 feet but it did not rise in the well but other borings in the same desert of variable depth between 50 and 300 feet and which passed through alternations of sand clay and delicious rock yielded water at the surface the rise and overflow of the water in artesian wells is generally referred and apparently with reason to the same principle as the play of an artificial fountain let the porous stratum or set of strata a a rest on the impermeable rock d and be covered by another mass of an impermeable nature the whole mass a a may easily in such a position become saturated with water which may descend from its higher and exposed parts a hilly region to which clouds are attracted and where rain falls in abundance suppose that at some point as at b and opening be made which gives a free passage upwards to the waters confined in a a at so low a level that they are subjected to the pressure of a considerable column of water collected in the more elevated portion of the same stratum the water will then rush out just as the liquid from a large barrel which is tapped and it will rise to a height corresponding to the level of its point of departure or rather to a height which balances the pressure previously exerted by the confined waters against the roof and sides of the stratum or reservoir a a in like manner if there happens to be a natural fissure sea a spring will be produced at the surface on precisely the same principle among the causes of the failure of artesian wells we may mention those numerous rents and faults which abound in some rocks and the deep ravines and valleys by which many countries are traversed for when these natural lines of drainage exist there remains a small quantity only of water to escape by artificial issues we are also liable to be baffled by the great thickness either of porous or impervious strata or by the dip of the beds which may carry off the waters from the adjoining highlands to some trough in an opposite direction as when the borings are made at the foot of an escarpment where the strata incline inwards or in a direction opposite to the face of the cliffs the mere distance of hills or mountains need not discourage us from making trials for the waters which fall on these higher lands readily penetrate to great doubts through highly inclined or vertical strata or through the fissures of shattered rocks and after flowing for a great distance must often re ascend and be brought up again by other fissures so as to approach the surface in the lower country here they may be concealed beneath the covering of undisturbed horizontal beds which it may be necessary to pierce in order to reach them it should be remembered that the course of waters flowing underground bears but a remote resemblance to that of rivers on the surface there being in the one case a constant descent from a higher to a lower level from the source of the stream to the sea whereas in the other the water may at one time sink far below the level of the ocean and afterwards rise again high above it among other curious facts ascertained by aid of the borer it is proved that in strata of different ages and compositions there are often open passages by which the subterranean waters circulate thus at St. Owen in France five distinct sheets of water were intersected in a well and from each of these a supply obtained in the third water bearing stratum at the depth of 150 feet a cavity was found in which the borer fell suddenly about a foot and since the water ascended in great volume the same falling of the instrument as in a hollow space has been remarked in england and other countries at tours in 1830 a well was perforated quite through the chalk when the water suddenly brought up from a depth of 364 feet a great quantity of fine sand with much vegetable matter and shells branches of a thorn several inches long much blackened by their stay in the water were recognized as also the stems of marsh plants and some of their roots which were still white together with the seeds of the same in a state of preservation which showed that they had not remained more than three or four months in the water among the seeds were those of the marsh plant gallium ooligan awesome and among the shells of freshwater species planorbas marginatus and some land species as helix rotundata and H. striata mesur duhardin who with others observed this phenomenon supposes that the waters had flowed from some valleys of avern or the vivare since the preceding autumn and analogous phenomenon is recorded at rimke near boschum in west failure where the water of an artesian well brought up from a depth of 156 feet several small fish three or four inches long the nearest streams in the country being at a distance of some leagues in both cases it is evident that water had penetrated to great depths not simply by filtering through a porous mass for then it would have left behind the shells fish and fragments of plants but by flowing through some open channels in the earth such examples may suggest the idea that the leaky beds of rivers are often the feeders of springs end of chapter 16 part 1