 Section 47 of Principles of Geology. This is a LibriVox recording. A LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org, recording by Dion Jones, Salt Lake City, Utah. Principles of Geology by Charles Lyall, Chapter 19, Part 5, Dorsetshire, Devonshire. At Lyme Regis in Dorsetshire, the church cliffs, as they are called, consisting of Leos, about 100 feet in height, gradually fell away at the rate of one yard a year from 1800 to 1829. An extraordinary landslip occurred on the 24th of December, 1839, on the coast between Lyme Regis and Axemouth, which has been described by the reverend W. D. Coneybear to whose kindness I am indebted for the accompanying section. The tract of downs ranging there along the coast is capped by chalk, which rests on sandstone, alternating with chert, beneath which is more than 100 feet of loose sand with concretions at the bottom, and belonging to the green sand formation, the whole of the above masses reposing on retentive beds of clay, belonging to the Leos, which shelves towards the sea. Numerous springs issuing from the loose sand have gradually removed portions of it and thus undermined the superstratum, so as to have caused subsidences at former times and to have produced a line of undercliff. In 1839 and excessively wet season had saturated all the rocks with moisture, so as to increase the weight of the incumbent mass, from which the support had already been withdrawn by the action of springs. Thus the superstrata were precipitated into hollows, prepared for them, and the adjacent masses of partially undermined rock to which the movement was communicated were made to slide down on a slippery basis of watery sand towards the sea. These causes gave rise to a convulsion which began on the morning of the 24th of December with a crashing noise, and on the evening of the same day fissures were seen opening in the ground and the walls of tenements rending and sinking until a deep chasm or ravine was formed, extending nearly three quarters of a mile in length, with a depth of from 100 to 150 feet, and a breadth exceeding 240 feet. At the bottom of this deep gulf lie fragments of the original surface thrown together in the wildest confusion. In consequence of lateral movements, the tract intervening between the new fissure and the sea, including the ancient undercliff, was fractured, and the whole line of sea-cliff carried bodily forwards for many yards. A remarkable pyramidal crag off Culver Hole Point, which lately formed a distinguishing landmark, has sunk from a height of about 70 to 20 feet, and the main cliff before more than 50 feet distant from this insulated crag is now brought almost close to it. This motion of the sea-cliff has produced a farther effect which may rank among the most striking phenomena of this catastrophe. The lateral pressure of the descending rocks has urged the neighboring strata, extending beneath the shingle of the shore, by their state of unnatural condensation, to burst upwards in a line parallel to the coast, thus an elevated ridge more than a mile in length and rising more than 40 feet, covered by a confused assemblage of broken strata and immense blocks of rock invested with seaweed and coralines and scattered over with shells and starfish and other productions of the deep forms an extended reef in front of the present range of cliffs. A full account of this remarkable landslip with a plan sections and many fine illustrative drawings was published by Mussors, Coneybear and Buckland. Cornwall. Near Penzance in Cornwall, there is a projecting tongue of land called the green formed of granitic sand from which more than 30 acres of pasture land have been gradually swept away in the course of the last two or three centuries. It is also said that St. Michael's Mount, now an insular rock, was formerly situated in a wood several miles from the sea, and its old cornish name, caraclaus, in cows, signifies, according to Carew, the whore rock in the wood. Between the mount and Newlen there is seen under the sand black vegetable mold full of hazelnuts and the branches leaves roots and trunks of forest trees all of indigenous species. This stratum has been traced seaward as far as the ebb permits and many proofs of a submerged vegetable accumulation with stumps of trees in the position in which they grew have been traced, says Sir Henry de la Bache, round the shores of Devon, Cornwall, and western Somerset. The facts not only indicate a change in the relative level of the sea and land since the species of animals and plants were the same as those now living in this district, but what is very remarkable there seems evidence of the submergence having been affected, in part at least, since the country was inhabited by man. A submarine forest occurring at the mouth of the parrot in Somerset sure on the south side of the Bristol Channel was described by Mr. L. Horner in 1815 and its position attributed to subsidence, a bed of peat is there seen below the level of the sea and the trunks of large trees such as the oak and ewe having their roots still diverging as they grew and fixed in blue clay. Tradition of loss of land in Cornwall. The oldest historians mention a tradition in Cornwall of the submersion of the lioness a country said to have stretched from the land's end to the silly islands. The tract if it existed must have been 30 miles in length and perhaps 10 in breadth. The land now remaining on either side is from 200 to 300 feet high. The intervening sea about 300 feet deep. Although there is no authentic evidence for this romantic tale it probably originated in some former inroads of the Atlantic accompanying perhaps a subsidence of land on this coast west coast of England. Having now brought together an ample body of proofs of the destructive operations of the waves tides and currents on our eastern and southern shores it will be unnecessary to enter into details of changes on the western coast for they present merely a repetition of the same phenomena and in general on an inferior scale on the borders of the estuary of the southern the flats of Somersetshire and Gloucestershire have received enormous accessions while on the other hand the coast of Sushire between the rivers Mercy and D has lost since the year 1764 many hundred yards and some affirm more than half a mile by the advance of the sea upon the abrupt cliffs of red clay and morals within the period above mentioned several lighthouses have been successively abandoned there are traditions in Pembroke sure and cardigan sure of far greater losses of territory than that which the lioness tale of Cornwall pretends to commemorate they are all important as demonstrating that the earliest inhabitants were familiar with the phenomenon of incursions of the sea loss of land on the coast of France the french coast particularly that of britney where the tides rise to an extraordinary height is the constant prey of the waves in the ninth century many villages and woods are reported to have been carried away the coast undergoing great change whereby the hill of saint michael was detached from the mainland the parish of borneuf and several others in that neighborhood were overflowed in the year 1500 in 1735 during a great storm the ruins of paulnell were seen uncovered in the sea end of chapter 19 part five chapter 20 of principles of geology this is a libre vox recording all libre vox recordings are in the public domain for more information or to volunteer please visit libre vox.org principles of geology by charles lyle chapter 20 action of tides and currents continued inroads of the sea at the mouths of the rine in holland changes in the arms of the rine proofs of subsidence of land estuary of the bee sposo formed in 1421 zotter z in the 13th century islands destroyed delta of the eames converted into a bay estuary of the dullard formed encroachment of the sea on the coast of slesfolk on shores of north america tidal wave called the boar influence of tides and currents on the mean level of seas action of currents in inland lakes and seas Baltic simbrian deluge straits of Gibralda no wonder current there weather salt is precipitated in the Mediterranean waste of shores of Mediterranean inroads of the sea at the mouths of the rine the line of british coast considered in the preceding chapter offered no example of the conflict of two great antagonistic forces the influx on the one hand of a river draining a large continent and on the other the action of the waves tides and currents of the ocean but when we pass over by the straits of dover to the continent and proceed northeastwards we find an admirable illustration of such a contest where the ocean and the rine are opposed to each other each disputing the ground now occupied by holland the one striving to shape out an estuary the other to form a delta there was evidently a period when the river obtained the ascendancy when the shape and perhaps the relative level of the coast and set of the tides were very different but for the last 2000 years during which man has witnessed and actively participated in the struggle the result has been in favor of the ocean the area of the whole territory having become more and more circumscribed natural and artificial barriers having given way one after the other and many hundred thousand human beings having perished in the waves changes in the arms of the rine the rine after flowing from the grissen alps copiously charged with sediment first purifies itself in the lake of constants where a large delta is formed then swelled by the r and numerous other tributaries it flows for more than 600 miles towards the north when entering a low tract it divides into two arms about 10 miles northeast of cleaves a point which must therefore be considered the head of its delta in speaking of the delta I do not mean to assume that all that part of holland which is comprised within the several arms of the rine can be called a delta in the strictest sense of the term because some portion of the country thus circumscribed as for example a part of Gelderland and Utrecht consists of strata which may have been deposited in the sea before the rine existed these older tracts may either have been raised like the ula bund and kuc during the period when the sediment of the rine was converting a part of the sea into land or they may have constituted islands previously the dark tint between antwerp and newport represents part of the netherlands which was land in the time of the romans then overflowed by the sea before and during the fifth century and afterwards reconverted into land when the river divides north of cleaves the left arm takes the name of the wall and the right retaining that of the rine is connected a little further to the north by an artificial canal with the river isle the rine then flowing westward divides again southeast of Utrecht and from this point it takes the name of the lec a name which was given to distinguish it from the northern arm called the old rine which was sanded up until the year 1825 when a channel was cut for it by which it now enters the sea at catwick it is common in all great deltas that the principal channels of discharge should shift from time to time but in holland so many magnificent canals have been constructed and have so diverted from time to time the course of the waters that the geographical changes in this delta are endless and their history since the roman era forms a complicated topic of antiquarian research the present head of the delta is about 40 geographical miles from the nearest part of the gulf called the zotter z and more than twice that distance from the general coastline the present head of the delta of the nile is about 80 or 90 geographical miles from the sea that of the ganji says before stated 220 and that of the mississippi about 180 reckoning from the point where the achafalaya branches off to the extremity of the new tongue of land in the gulf of mexico but the comparative distance between the heads of deltas and the sea affords no positive data for estimating the relative magnitude of the alluvial tracts formed by their respective rivers for the ramifications depend on many varying in temporary circumstances and the area over which they extend does not hold any constant proportion to the volume of water in the river the rime therefore has at present three mouths about two-thirds of its waters flow to the sea by the wall and the remainder is carried partly to the zotter z by the easel and partly to the ocean by the lake as the whole coast to the south as far as austen and on the north to the entrance of the baltic has with few exceptions from time immemorial yielded to the force of the waves it is evident that the common delta of the rime use and shelt for these three rivers may all be considered as discharging their waters into the same part of the sea would if its advance had not been checked have become extremely prominent and even if it had remained stationary would long air this have projected far beyond the rounded outline of the coast like that strip of land already described at the mouth of the mississippi but we find on the contrary that the islands which skirt the coast have not only lessened in size but in number also while great bays have been formed in the interior by incursions of the sea in order to explain the incessant advance of the ocean on the shores and inland country of holland man sure elidibo mod has suggested that there is in all probability been a general depression or sinking of the land below its former level over a wide area such a change of level would enable the sea to break through the ancient line of sand banks and islands which protected the coast would lead to the enlargement of bays the formation of new estuaries and ultimately to the entire submergence of land these views appear to be supported by the fact that several peat mosses of freshwater origin now occur under the level of the sea especially on the site of the zotter z and lake flavo presently to be mentioned several excavations also made for wells at utrekt amsterdam and rotterdam have proved that below the level of the ocean the soil near the coast consists of alternations of sand with marine shells and beds of peat and clay which have been traced to the depth of 50 feet and upwards i have said that the coast to the south as far as ostent has given way this statement may at first seem opposed to the fact that the tract between antwerp and newport shaded black in the in next map of figure 38 although now dry land and supporting a large population has within the historical period been covered with the sea this region however consisted in the time of the romans of woods marshes and peat mosses protected from the ocean by a chain of sandy dunes which were afterwards broken through during storms especially in the fifth century the waters of the sea during these eruptions threw down upon the barren peat a horizontal bed of fertile clay which is in some places three yards thick full of recent shells and works of art the inhabitants by the aid of embankments and the sand dunes of the coast have succeeded although not without frequent disasters in defending the soil thus raised by the marine deposit inroads of the sea in holland if we pass to the northward of the territory just alluded to and cross the shelf we find that between the 14th and 18th centuries parts of the islands of walterin and beveland were swept away and several populist districts of tadsand losses which far more than counterbalance the gain of land caused by the sanding up of some pre-existing creeks in 1658 the island orison was annihilated one of the most memorable inroads of the sea occurred in 1421 when the tide pouring into the mouth of the united muse and while burst through a dam in the district between dort and kurtrudenberg and overflowed 72 villages forming a large sheet of water called the bee's bosh see map figure 38 35 of the villages were irretrievably lost and no vestige even of their ruins was afterwards seen the rest were redeemed and the site of the others though still very generally represented on maps as an estuary has in fact been gradually filled up by alluvial deposits and had become in 1835 as i was informed by professor mall an immense plain yielding abundant crops of hay though still uninhabited to the north of the muse is a long line of shore covered with sand dunes where great encroachments have taken place from time to time in consequence chiefly of the prevalence of southeasterly winds which blow down the sands toward the sea the church of chevon ingan not far from the hag was once in the middle of the village and now stands on the shore half the place having been overwhelmed by the waves in 1570 catwick once far from the sea is now upon the shore two of its streets having been overflowed and land torn away to the extent of 200 yards in 1719 it is only by the aid of embankments that paton and several other places further north have been defended against the sea formation of the zowder z and straits of staveron still more important are the changes which have taken place on the coast opposite the right arm of the rine or the easel where the ocean has burst through a large isthmus and entered the inland lake flavo which in ancient times was according to pomponius milla formed by the overflowing of the rine over certain lowlands it appears that in the time of tacitus there were several lakes on the present site of the zowder z between freeslan and holland the successive inroads by which these and a great part of the adjoining territory were transformed into a great gulf began about the commencement and were completed toward the close of the 13th century alting gives the following relation of the occurrence drawn from manuscript documents of contemporary inhabitants of the neighboring provinces in the year 1205 the island now called veering in to the south of the texel was still a part of the mainland but during several high floods of which the dates are given ending in December 1251 it was separated from the continent by subsequent incursions the sea consumed great parts of the rich and populous isthmus a low tract which stretched on the north of lake flavo between stavrin in freesland and middenblick in holland till at length a breach was completed about the year 1282 and afterwards widened great destruction of land took place when the sea first broke in and many towns were swept away but there was afterwards a reaction to a certain extent large tracts at first submerged having been gradually redeemed the new straits south of stavrin are more than half the width of those of dover but are very shallow the greatest depth not exceeding two or three fathoms the new bays of a somewhat circular form and between 30 and 40 miles in diameter how much of this space may formally have been occupied by lake flavo is unknown destruction of islands a series of islands stretching from the texel to the mouths of the visor and elba are probably the last relics of a tract once continuous they have greatly diminished in size and have lost about a third of their number since the time of pliny for that naturalist counted 23 islands between texel and eider whereas now there are only 16 including heligoland and newark the island of heligoland at the mouth of the elba consists of a rock of red marl of the koi preformation of the germans and is bounded by perpendicular red cliffs about 200 feet high although according to some accounts it has been greatly reduced in size since the year 800 mr. weebel assures us that the ancient map by mayer cannot be depended upon and that the island according to the description still extant by adam of premon was not much larger than now in the time of charlemagne on comparing the map made in the year 1793 by the danish engineer of asel the average encroachment of the sea on the cliffs between that period in the year 1848 or about half a century did not amount to more than three feet on the other hand some few islands had extended their bounds in one direction or became connected with others by the sanding up of channels but even these like juiced have generally given way as much on the north towards the sea as they have gained on the south or land side the dollard formed while the delta of the rine has suffered so materially from the movements of the ocean it can hardly be supposed that minor rivers on the same coast should have been permitted to extend their deltas it appears that in the time of the romans there was an alluvial plane of great fertility where the m's entered the sea by three arms this slow country stretched between grenicant and freesland and sent out a peninsula to the northeast towards emden a flood in 1277 first destroyed part of the peninsula other inundations followed at different periods throughout the 15th century in 1507 a part only of torum a considerable town remained standing and in spite of the erection of dams the remainder of that place together with market towns villages and monasteries to the number of 50 were finally overwhelmed the new gulf which was called the dollard although small in comparison to the side of z occupied no less than six square miles at first but part of the space was in the course of the two following centuries again redeemed from the sea the small bay of leibucht farther north was formed in a similar manner in the 13th century and the bay of haubucht in the middle of the 16th both of these have since been partially weak converted into dry land another new estuary called the gulf of yada near the mouth of the vaser scarcely inferior in size to the dollar has been gradually hollowed out since the year 1016 between which era and 1651 the space of about four square miles has been added to the sea the rivulet which now enters this inlet is very small but errands conjectures that an arm of the vaser had once an outlet in that direction coast of sleswig farther north we find so many records of waste on the western coast of sleswig is to lead us to anticipate that at no distant period in the history of the physical geography of europe jutland may become an island and the ocean may obtain a more direct entrance into the baltek indeed the temporary insulation of the northern extremity of jotland has been affected no less than four times within the records of history the ocean having as often made a breach through the bar of sand which usually excludes it from the lean fjord this long frith is 120 miles in length including its wingings and communicates at its eastern end with the baltek the last eruption of salt water happened in 1824 and the fjord was still open in 1837 when some vessels of 30 tons burden passed through the marsh islands between the rivers elba and eider are mere banks like the lands formed of the warp in the humber protected by dykes some of them after having been inhabited with security for more than 10 centuries have been suddenly overwhelmed in this manner in 1216 no less than 10 000 of the inhabitants of eidersted and dick marsh perished and on the 11th of october 1634 the islands and the whole coast as far as jotland suffered by a dreadful deluge destruction of north strand by the sea north strand up to the year 1240 was with the islands of silt and fur so nearly connected with the mainland as to appear a peninsula and was called north freeze land a highly cultivated populous district it measured from 9 to 11 geographical miles from north to south and 6 to 8 from east to west in the above mentioned year it was torn asunder from the continent and in part overwhelmed the isle of north strand thus formed was towards the end of the 16th century only four geographical miles in circumference and was still celebrated for its cultivation and numerous population after many losses it still contained 9 000 inhabitants at last in the year 1634 on the evening of the 11th of october a flood passed over the whole island whereby 1300 houses with many churches were lost 50 000 head of cattle perished and above 6000 men three small islets one of them still called north strand alone remained which are now continually wasting the redundancy of river water in the Baltic especially during the melting of ice and snow in spring causes in general an outward current through the channel called the catagod but after a continuance of north westerly gales especially during the height of the spring tides the Atlantic rises and pouring a flood of water into the Baltic commits dreadful devastations on the aisles of the Danish archipelago this current even acts though with diminished force as far eastward as the vicinity of Danzig accounts written during the last ten centuries attest the wearing down of promontories on the Danish coast the deepening of gulfs the severing of peninsulas from the mainland and the waste of islands while in several cases marshland defended for centuries by dykes has at last been overflowed and thousands of the inhabitants well in the waves thus the island bar so on the coast of Slesvik has lost year after year and acre at a time and the island alson suffers in like manner simbrian deluge as we have already seen that during the flood before mentioned 6,000 men and 50,000 head of cattle perished on north strand on the western coast of jotland we are all well prepared to find that this peninsula cimbrica ciasonisos of the ancients has from a remote period been the theater of like catastrophes accordingly Strabo records a story although he treats it as an incredible fiction that during a high tide the ocean rose upon this coast so rapidly that men on horseback were scarcely able to escape floris alluding to the same tradition says cimbri tutani at gt galini ab extremis galile profugi con teras irum in udasit oceanis novus sedes toto or be querebant this event commonly called the simbrian deluge is supposed to have happened about three centuries before the christian era but it is not improbable that the principal catastrophe was preceded and followed by many devastations like those experienced in modern times on the islands and shores of jotland and such calamities may well be conceived to have forced on the migration of some maritime tribes inroads of the sea on the eastern shores of north america after so many authentic details respecting the destruction of the coast in parts of europe best known it will be unnecessary to multiply examples of 332 analogous changes in more distant regions of the world it must not however be imagined that our own seas form any exception to the general rule thus for example if we pass over to the eastern coast of north america where the tides rise in the bay of fundy to great elevation we find many facts testing the incessant demolition of land cliffs often several hundred feet high composed of sandstone red moral and other rocks which border that bay and its numerous estuaries are perpetually undermined the ruins of these cliffs are gradually carried in the form of mud sand and large boulders into the atlantic by powerful currents aided at certain seasons by drift ice which form along the coast and freezes round large stones that cape may on the north side of delaware bay in the united states the encroachment of the sea was shown by observations made consecutively for 16 years from 1804 to 1820 to average about nine feet a year and at sullivan's island which lies on the north side of the entrance of the harbor of charleston in south carolina the sea carried away a quarter of a mile of land in three years ending in 1786 tidal wave called the bore before concluding my remarks on the actions of the tides i must not omit to mention the wave called the bore which is sometimes produced in a river where a large body of water is made to rise suddenly in consequence of the contraction of the channel this wave terminates abruptly on the inland side because the quantity of water contained in it is so great and its motion so rapid that time is not allowed for the surface of the river to be immediately raised by means of transmitted pressure a tide wave thus rendered abrupt has a close analogy observes mr. waywell to the waves which curl over and break on a shelving shore the bore which enters the seven where the phenomenon is of almost daily occurrence is sometimes nine feet high and at spring tides rushes up the estuary with extraordinary rapidity the finest example which i have seen of this wave was at novus scotia where the tide is said to rise in some places 70 feet perpendicular to be the highest in the world in the large estuary of the shubinikete which connects with another estuary called the basin of mines itself in branchment of the bay of fundy a vast body of water comes rushing up with a roaring noise into a long narrow channel and while it is ascending as all the appearance of pouring down a slope as steep as that of the celebrated rapids of the st. Lawrence in picturesque effect however it bears no comparison for instead of the transparent green water and snow white foam of the st. Lawrence the whole current of the shubinikete is turbid and densely charged with red mud the same phenomenon is frequently witnessed in the principal branches of the ganges and in the magna as before mentioned on page 279 in the hoogley says renal the bore commences at hoogley point the place where the river first contracts itself and is perceptible above hoogley town and so quick is its motion that it hardly employs four hours in traveling from one to the other though the distance is nearly 70 miles at calcutta it sometimes occasions an instantaneous rise of five feet and both here and in every other part of its track the boats on its approach immediately quit to shore and make for safety to the middle of the river in the channels between the islands in the mouth of the magna the height of the bore is said to exceed 12 feet and is so terrific in its appearance and dangerous in its consequences that no boat will venture to pass at spring tide these waves may sometimes cause inundations undermine cliffs and still more frequently sweep away trees and land animals from low shores so that they may be carried down and ultimately embedded in fluvia tile or submarine deposits in such large bodies of water as the north american lakes the continuance of a strong wind in one direction often causes the elevation of the water and its accumulation on the leeward side and while the equilibrium is restoring itself powerful currents are occasioned in october 1833 a strong current in lake eerie caused partly by the set of the waters towards the outlet of the lake and partly by the prevailing wind burst a passage through the extensive peninsula called longpoint and soon excavated a channel more than nine feet deep 900 feet wide its width and depth have since increased and a new and costly pier has been erected for it is hoped that this event will permanently improve the navigation of lake eerie for steamboats on the opposite or southern coast of this lake in front of the town of cleveland the degradation of the cliffs have been so rapid for several years preceding a survey made in 1837 as to threaten many towns with demolition in the black sea also although free from tides we learn from palos that there is a sufficiently strong current to undermine the cliffs in many parts and particularly in the chromia straits of gibraltar it is well known that a powerful current sets constantly from the atlantic into the Mediterranean and its influence extends along the whole southern borders of that sea and even to the shores of asia minor captain smith found during his survey that the central current ran constantly at the rate of from three to six miles an hour eastward into the Mediterranean the body of water being three miles and a half wide but there are also two lateral currents one on the european and one on the african side each of them about two miles and a half broad and flowing at about the same rate as the central stream these lateral currents ebb and flow with the tide setting alternately into the Mediterranean and into the atlantic the excess of water constantly flowing in is very great and there is only one cause to which this can be attributed the loss of water in the Mediterranean by evaporation that the level of this sea should be considerably depressed by this cause is quite conceivable since we know that the winds blowing from the shores of Africa are hot and dry and hygrometrical experiments recently made in Malta and other places show that the mean quantity of moisture in the air investing the Mediterranean is equal only to one half of that in the atmosphere of england the temperature also of the great inland sea is upon an average higher by three and a half degrees of fahrenheit than the eastern part of the atlantic ocean in the same latitude which must greatly promote its evaporation the black sea being situated in a higher latitude and being the receptacle of rivers flowing from the north is much colder and its expenditure far less accordingly it does not draw any supply from the Mediterranean but on the contrary contributes to it by a current flowing outwards for the most part of the year through the Dardanelles the discharge however at the Bosphorus is so small when compared to the volume of water carried in by rivers as to imply a great amount of evaporation in the black sea weather salt be precipitated in the Mediterranean it is however objected that evaporation carries away only fresh water and that the current from the atlantic is continually bringing in salt water why then do not the component parts of the waters of the Mediterranean vary or how can they remain so nearly the same as those of the ocean some have imagined that the excess of salt might be carried away by an undercurrent running in a contrary direction to the superior and this hypothesis appeared to receive confirmation from a late discovery that the water taken up about 50 miles within the straits from a depth of 670 fathoms contained a quantity of salt four times greater than the water on the surface Dr. Walliston who analyzed this water obtained by Captain Smith truly inferred that an undercurrent of such denser water flowing outward if of equal breadth and depth with the current near the surface would carry out as much salt below as is brought in above although it moved with less than one fourth part of the velocity and would thus prevent a perpetual increase of saltiness in the Mediterranean beyond that existing in the Atlantic it was also remarked by others that the result would be the same if the swiftness being equal the inferior current had only one fourth of the volume of the superior at the same time there appeared reason to conclude that this great specific gravity was only acquired by water at immense depths for two specimens of the water taken within the Mediterranean at the distance of some hundred miles from the straits and at depths of 400 and even 450 fathoms were found by Dr. Walliston not to exceed in density that of many ordinary samples of seawater such being the case we can now prove that the vast amount of salt brought into the Mediterranean does not pass out again by the straits for it appears by Captain Smith's soundings which Dr. Walliston had not seen that between the capes of Trafalgar and Spartel which are 22 miles apart and where the straits are shallowest the deepest part which is on the side of Cape Spartel is only 220 fathoms it is therefore evident that if water sinks in certain parts of the Mediterranean in consequence of the increase of its specific gravity to greater depths than 220 fathoms it can never flow out again into the Atlantic since it must be stopped by the submarine barrier which crosses the shallowest part of the straits of Gibraltar the idea of the existence of a countercurrent at a certain depth first originated in the following circumstances Mishir Diego commander of a privateer called the Phoenix of Marseille gave chase to a Dutch merchant ship near Cuita Point and coming up with her in the middle of the gut between Tarifa and Tangier gave her one broadside which directly sunk her a few days after the sunken ship with her cargo of brandy and oil was cast ashore near Tangier which is at least four leagues to the westward of the place where she went down and to which she must have floated in a direction contrary to the course of the central current this fact however affords no evidence of an undercurrent because the ship when it approached the coast would necessarily be within the influence of a lateral current which running westward twice every 24 hours might have brought back the vessel to Tangier what then becomes of the excess of salt for this is an inquiry of the highest geological interest the Roan the Poe the Nile and many hundred minor streams and springs pour annually into the Mediterranean large quantities of carbonate of lime together with iron, magnesium, silica, alumina, sulfur, and other mineral ingredients in a state of chemical solution to explain why the influx of this matter does not alter the composition of the sea has never been regarded as a difficulty for it is known that calcareous rocks are forming in the delta of the Roan in the Adriatic on the coast of Asia Minor and in other localities precipitation is acknowledged to be the means whereby the surplus mineral matter is disposed of after the consumption of a certain portion in the secretions of zoophytes and other marine animals but before myriad of soda can in like manner be precipitated the whole Mediterranean ought according to the received principles of chemistry to become as much saturated with salt as Lake Arau the Dead Sea or the brine springs of Cheshire it is undoubtedly true in regard to small bodies of water that every particle must be fully saturated with myriad of soda before a single crystal of salt can be formed such is probably the case in all natural sultans such for example is those described by travelers as occurring on the western borders of the Black Sea where extensive marshes are said to be covered by thin films of salt after a rapid evaporation of seawater the salt atongs of the Roan where salt has sometimes been precipitated in considerable abundance have been already mentioned in regard to the depth of the Mediterranean it appears that between Gibraltar and Ciuta Captain Smith sounded to the enormous depth of 950 fathoms and found there a gravelly bottom with fragments of broken shells saucer a sounded to the depth of 2000 feet within a few yards of the shore at Nice and Mishir Birad has lately fathomed to the depth of more than 6000 feet in several places without reaching the bottom the central abysses therefore of this sea are in all likelihood at least as deep as the Alps are high and as at the depth of 700 fathoms only water has been found to contain a proportion of salt four times greater than that at the surface we may presume that the excess of salt may be much greater at the depth of two or three miles after evaporation the surface becomes impregnated with a slight excess of salt and its specific gravity being less increased it instantly falls to the bottom while lighter water rises to the top or flows in laterally being always supplied by rivers and the current from the Atlantic the heavier fluid when it arrives at the bottom cannot stop if it can gain access to any lower part of the bed of the sea not previously occupied by water of the same density how far this accumulation of brine can extend before the inferior strata of water will part with any of their salt and what difference in such a chemical process the immense pressure of the incumbent ocean or the escape of heated vapours thermal springs or submarine volcanic eruptions might occasion our questions which cannot be answered in the present state of science the Straits of Gibraltar are said to become gradually wider by the wearing down of the cliffs on each side at many points and the current sets along the coast of Africa so as to cause considerable inroads in various parts particularly near Carthage near the canopic mouth of the Nile at Abukir the coast was greatly devastated in the year 1784 when a small island was nearly consumed by a series of similar operations the old site of the cities of Necropolis Tapasiris Parva and Canopus have become a sand bank end of chapter 22 section 49 of principles of geology this is a LibriVox recording a LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Diongeines Salt Lake City Utah principles of geology by Charles Lyle chapter 21 reproductive effects of tides and currents estuaries how formed silting up of estuaries does not compensate the loss of land on the borders of the ocean bed of the German ocean composition and extent of its sandbanks strata deposited by currents in the English Channel on the shores of the Mediterranean at the mouths of the Amazon Orinoco and Mississippi wide area over which strata may be formed by this cause from the facts enumerated in the last chapter it appears that on the borders of the ocean currents and tides cooperating with the waves of the sea are most powerful instruments in the destruction and transportation of rocks and as numerous tributaries discharge their alluvial burden into the channel of one great river so we find that many rivers deliver their earthly contents to one marine current to be borne by it to a distance and deposited in some deep receptacle of the ocean the current besides receiving this tribute of sedimentary matter from streams draining the land acts also itself on the coast as does a river on the cliffs which bound a valley yet the waste of cliffs by marine currents constitutes on the whole a very insignificant portion of the denudation annually affected by aqueous causes as i shall point out in the sequel of this chapter in inland seas where the tides are insensible or on those parts of the borders of the ocean where they are feeble it is scarcely possible to prevent a harbor at a river's mouth from silting up for a bar of sand or mud is formed at points where the velocity of the turbid river is checked by the sea or where the river and a marine current neutralize each other's force for the current as we have seen may like the river hold in suspension a large quantity of sediment or cooperating with the waves may cause the progressive motion of a shingle beach in one direction i have already alluded to the erection of piers and groins at certain places on our southern coast to arrest the course of the shingle and sand the immediate effect of these temporary obstacles is to cause a great accumulation of pebbles on one side of the barrier after which the beach still moves on round the end of the pier at a greater distance from the land this system however is often attended with a serious evil for during storms the waves throw suddenly into the harbor the vast heap of pebbles which have collected for years behind the groin or pier as happened during a great gale january 1839 at dover the formation and keeping open of large estuaries are due to the combined influence of tidal currents and rivers for when the tide rises a large body of water suddenly enters the mouth of the river where becoming confined within narrower bounds while its momentum is not destroyed it is urged on and having to pass through a contracted channel rises and runs with increased velocity just as a stream when it reaches the arch of a bridge scarcely large enough to give passage to its waters rushes with a steep fall through the arch during the ascent of the tide a body of fresh water flowing down in an opposite direction from the higher country is arrested in its course for several hours and thus a large lake of fresh and brackish water is accumulated which when the sea ebbs is let loose as on the removal of an artificial sleuths or dam by the force of this retiring water the alluvial sediment both of the river and of the sea is swept away and transported to such a distance from the mouth of the estuary that a small part only can return with the next tide it sometimes happens that during a violent storm a large bar of sand is suddenly made to shift its position so as to prevent the free influx of the tides or efflux of river water thus about the year 1500 the sands at bayone were suddenly thrown across the mouth of the ador that river flowing back upon itself soon forced a passage to the northward along the sandy plain of cap retin till at last it reached the sea at buca at the distance of seven leagues from the point where it had formerly entered it was not till the year 1579 that the celebrated architect louis defoe undertook at the desire of henry the third to reopen the ancient channel which he at last affected with great difficulty in the estuary of the tames at london and in the gerund the tide rises only for five hours and ebbs seven and in all estuaries the water requires a longer time to run down then up so that the preponderating force is always in the direction which tends to keep open a deep and broad passage but for reasons already explained there is naturally a tendency in all estuaries to silt up partially since eddies and backwaters and points where opposing streams meet are very numerous and constantly change their position many writers have declared that the gain on our eastern coast since the earliest periods of history has more than counterbalanced the loss but they have been at no pains to calculate the amount of loss and have often forgotten that while the new acquisitions are manifest there are rarely any natural monuments to attest the former existence of the land that has been carried away they have also taken into their account those tracks artificially recovered which are often of great agricultural importance and may remain secure perhaps for thousands of years but which are only a few feet above the mean level of the sea and are therefore exposed to be overflowed again by a small proportion of the force required to move cliffs of considerable height on our shores if it were true that the area of land annually abandoned by the sea in estuaries were equal to that invaded by it there would still be no compensation in kind the tidal current which flows out from the northwest and bears against the eastern coast of england transports as we have seen materials of various kinds aided by the waves it undermines and sweeps away the granite niece trap rocks and sandstone of shetland and removes the gravel and loam of the cliffs of holderness norfolk and suffolk which are between 20 and 300 feet in height and which waste at various rates of from one foot to six yards annually it also bears away in cooperation with the tames and the tides the strata of london clay on the coast of essyx and shepi the sea at the same time consumes the chalk with its flints for many miles continuously on the shores of kent and sussex commits annual ravages on the freshwater beds capped by a thick covering of chalk flint gravel in hampshire and continually saps the foundations of the portland limestone it receives besides during the rainy months large supplies of pebbles sand and mud which numerous streams from the grampians cheviots and other chains send down to the sea to what regions then is all this matter consigned it is not retained in mechanical suspension by the waters of the ocean nor does it mix with them in a state of chemical solution it is deposited somewhere yet certainly not in the immediate neighborhood of our shores for in that case there would soon be a cessation of the encroachment of the sea and large tracks of low land like romney marsh would almost everywhere encircle our island as there is now a depth of water exceeding 30 feet in some spots where towns like dunwich flourished but a few centuries ago it is clear that the current not only carries far away the materials of the wasted cliffs but is capable also of excavating the bed of the sea to a certain moderate depth so great is the quantity of matter held in suspension by the tidal current on our shores that the waters are in some places artificially introduced into certain lands below the level of the sea and by repeating this operation which is called warping for two or three years considerable tracks have been raised in the estuary of the Humber to the height of about six feet if a current charged with such materials meets with deep depressions in the bed of the ocean it must often fill them up just as a river when it meets with a lake in its course fills it gradually with sediment I have said that the action of the waves and currents on sea cliffs or their power to remove matter from above to below the sea level is insignificant in comparison with the power of rivers to perform the same task as an illustration we may take the coast of holderness described in the last chapter it is composed as we have seen a very destructible materials is 36 miles long and its average height may be taken at 40 feet as it has wasted away at the rate of two and a quarter yards annually for a long period it will be found on calculation that the quantity of matter thrown down into the sea every year and removed by the current amounts to 51,321,600 cubic feet it has been shown that the united Ganges and Brahmaputra carry down to the Bay of Bengal 40 billion of cubic feet of solid matter every year so that their transporting power is no less than 780 times greater than that of the sea on the coast above mentioned and in order to produce a result equal to that of the two Indian rivers we must have a line of wasting coast like that of holderness nearly 28,000 miles in length or longer than the entire circumference of the globe by above 3000 miles the reason of so great a difference in the results may be understood when we reflect that the operations of the ocean are limited to a single line of cliff surrounding a large area whereas great rivers with their tributaries and the mountain torrents which flow into them act simultaneously on a length of bank almost indefinite nevertheless we are by no means entitled to infer that the denuding force of the great ocean is a geological cause of small efficacy or inferior to that of rivers its chief influence is exerted at moderate depths below the surface on all those areas which are slowly rising or are attempting as it were to rise above the sea from data hitherto obtained respecting subterranean movements we can scarcely speculate on an average rate of upheaval of more than two or three feet in a century and elevation to this amount is taking place in Scandinavia and probably in many submarine areas as vast as those which we know to be sinking from the proofs derived from circular lagoon islands or coral atolls suppose strata as indestructible as those of the welden or the lower and upper cretaceous formation or the tertiary deposits of the british isles to be thus slowly upheaved how readily might they all be swept away by waves and currents in an open sea how entirely might each stratum disappear as it was brought up successively and exposed to the breakers shoals of wide extent might be produced but it is difficult to conceive how any continent could ever be formed under such circumstances were it not indeed for the hardness and toughness of the crystalline and volcanic rocks which are often capable of resisting the action of the waves few lands might ever emerge from the myths of an open sea supposed filling up of the german the german ocean is deepest on the norwegian side where the soundings give 190 fathoms but the mean depth of the whole basin may be stated at no more than 31 fathoms the bed of this sea is traversed by several enormous banks the greatest of which is the doger bank extending for upwards of 354 miles from north to south the whole superfaces of these shoals is equal to about one-third of the whole extent of england and scotland the average height of the banks measures according to mr stevensson about 78 feet the upper portion of them consisting of fine and coarse salicius sand mixed with comminuted corals and shells it had been supposed that these vast submarine hills were made up bodily of loose materials supplied from the waist of the english dutch and other coasts but the survey of the north sea conducted by captain huet affords ground for suspecting this opinion to be erroneous if such immense mounds of sand and mud had been accumulated under the influence of currents the same causes ought nearly to have reduced to one level the entire bottom of the german ocean instead of which some long narrow ravines are found to intersect the banks one of these varies from 17 to 44 fathoms in depth and has very precipitous sides in one part called the inner silver pits it is 55 fathoms deep the shallowest parts of the doger bank were found to be 42 feet underwater except in one place where the wreck of a ship had caused a shoal such uniformity in the minimum depth of water seems to imply that the currents which vary in their velocity from a mile to two miles and a half per hour have power to prevent the accumulation of drift matter in places of less depth strata deposited by currents it appears extraordinary that in some tracks of the sea adjoining the coast of england where we know that currents are not only sweeping along rocky masses thrown down from time to time from the high cliffs but also occasionally scooping out channels in the regular strata there should exist fragile shells and tender zoophytes in abundance which live uninjured by these violent movements the ocean however is in this respect a counterpart of the land and as on the continents rivers may undermine their banks uproot trees and roll along sand and gravel while their waters are inhabited by testacia and fish and their alluvial plains are adorned with rich vegetation and forests so the sea may be traversed by rapid currents and its bed may here and there suffer great local derangement without any interruption of the general order and tranquility it has been ascertained by soundings in all parts of the world that where new deposits are taking place in the sea coarse sand and small pebbles commonly occur near the shore while further from land and in deeper water finer sand and broken shells are spread out over the bottom still farther out the finest mud and ooze are alone met with mr austin observes that this rule holds good in every part of the english channel examined by him he also informs us that where the tidal current runs rapidly in what are called races where surface undulations are perceived in the calmest weather over deep banks the discoloration of the water does not arise from the power of such a current to disturb the bottom at a depth of 40 or 80 fathoms as some have supposed in these cases a column of water sometimes 500 feet in height is moving onwards with the tide clear and transparent above while the lower portion holds fine sediment in suspension a fact ascertained by soundings when suddenly it impinges upon a bank and its height is reduced to 300 feet it is thus made to boil up and flow off at the surface a process which forces up the lower strata of water charged with fine particles of mud which in their passage from the coast had gradually sunk to a depth of 300 feet or more one important character in the formations produced by currents is the immense extent over which they may be the means of diffusing homogenous mixtures for these are often co extensive with a great line of coast and by comparison with their deposits the deltas of rivers must shrink into significance in the Mediterranean the same current which is rapidly destroying many parts of the African coast between the straits of Gibraltar and the Nile checks also the growth of the delta of the Nile and drifts the sediment of that great river to the eastward to this source may be attributed the rapid accretions of land on parts of the Syrian shores where rivers do not enter among the greatest deposits now in progress and of which the distribution is chiefly determined by currents we may class those between the mouths of the Amazon and the southern coast of North America captain Sabine found that the equatorial current before mentioned was running with the rapidity of four miles an hour where it crosses the stream of the Amazon which river preserves part of its original impulse and has its waters not wholly mingled with those of the ocean at the distance of 300 miles from its mouth the sediment of the Amazon is thus constantly carried to the northwest as far as to the mouths of the orinoco and an immense tract of swamp is formed along the coast of Guiana with a long range of muddy shoals bordering the marshes and becoming converted into land the sediment of the orinoco is partly detained and settles near its mouth causing the shores of Trinidad to extend rapidly and is partly swept away into the Caribbean sea by the Guiana current according to Humboldt much sediment is carried again out of the Caribbean sea into the Gulf of Mexico it should not be overlooked that marine currents even on coasts where there are no large rivers may still be the agents of spreading not only sand and pebbles but the finest mud far and wide over the bottom of the ocean for several thousand miles along the western coast of South America comprising the larger parts of Peru and Chile there is a perpetual rolling of shingle along the shore part of which as mr Darwin has shown are incessantly reduced to the finest mud by the waves and swept into the depths of the Pacific by the tides and currents the same author however has remarked that notwithstanding the great force of the waves on that shore all rocks 60 feet underwater are covered by seaweed showing that the bed of the sea is not denuded at that depth the effects of the winds being comparatively superficial in regard to the distribution of sediment by currents it may be observed that the rate of subsidence of the finer mud carried down by every great river into the ocean or of that caused by the rolling of the waves upon a shore must be extremely slow for the more minute the separate particles of mud the slower will they sink to the bottom and the sooner will they acquire what is called their terminal velocity it is well known that a solid body descending through a resisting medium falls by the force of gravity which is constant but its motion is resisted by the medium more and more as its velocity increases until the resistance becomes sufficient to counteract the farther increase of velocity for example a leaden ball one inch diameter falling through air of density as at the earth's surface will never acquire greater velocity than 260 feet per second and in water its greatest velocity will be eight feet six inches per second if the diameter of the ball were one one hundredth of an inch the terminal velocities in air would be 26 feet and in water point eight six of a foot per second now every chemist is familiar with the fact that minute particles descend with extreme slowness through water the extent of their surface being very great in proportion to their weight and the resistance of the fluid depending on the amount of surface a precipitate of sulfate of barita for example will sometimes require more than five or six hours to subside one inch while oxalate and phosphate of lime require nearly an hour to subside about an inch and a half and two inches respectively so exceedingly small are the particles of which these substances consist when we recollect that the depth of the ocean is supposed frequently to exceed three miles and that currents run through different parts of that ocean at the rate of four miles an hour and when at the same time we consider that some fine mud carried away from the mouths of rivers and from sea beaches where there is a heavy surf as well as the impalpable powder showered down by volcanoes may subside at the rate of only an inch per hour we shall be prepared to find examples of the transportation of sediment over areas of indefinite extent it is not uncommon for the emery powder used in polishing glass to take more than an hour to sink one foot suppose mud composed of coarser particles to fall at the rate of two feet per hour and these to be discharged into that part of the gulf stream which preserves a mean velocity of three miles an hour for a distance of 2000 miles in 28 days these particles will be carried 2016 miles and will have fallen only to a depth of 224 fathoms in this example however it is assumed that the current retains its superficial velocity at the depth of 224 fathoms for which we have as yet no data although we have seen that the motion of a current may continue at the depth of 100 fathoms experiments should be made to ascertain the rate of currents at considerable distances from the surface and the time taken by the finest sediment to settle in seawater of a given depth and then the geologist may determine the area over which homogenous mixtures may be simultaneously distributed in certain seas end of chapter 21 chapter 22 part one 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 recording by Melpheor Raywood principles of geology by Charles Lyell section number 50 chapter 22 igneous courses changes of the inorganic world continued igneous courses division of the subject distinct volcanic regions region of the Andes system of volcanoes extending from the Aleutian isles to Malacca and Sunder islands Polynesian archipelago volcanic region extending from central Asia to the Azores tradition of the luges on the shores of the Bosphorus Hellespont and Grekin Isles periodical alternation of earthquakes in Syria and southern Italy western limits of the european region earthquakes rarer and more feeble as we recede from the centers of volcanic action extinct volcanoes not to be included in lines of active events we have hithero considered the changes wrought since the times of history and tradition by the continued action of aqueous courses on the earth's surface and we have next to examine those resulting from igneous agency as the rivers and springs on the land and the tides and currents in the sea have with some slight modifications been fixed and constant to certain localities from the earliest periods of which we have any records so the volcano and the earthquake have with few exceptions continued during the same laps of time to disturb the same regions but as there are signs on almost every part of our continent of great power having been exerted by running water on the surface of the land and by waves tides and currents on cliffs bordering the sea where in modern times no rivers have excavated and the waves or tidal currents undermined so we find signs of volcanic vents and violent subterranean movements in places where the action of fire or internal heat has long been dormant we can explain why the intensity of the force of aqueous causes should be developed in succession in different districts currents for example tides and the ways of the sea cannot destroy coasts shape out or split up estuaries break through isthmuses and annihilate islands form shoals in one place and remove them from another without the direction and the position of their destroying and transporting power becoming transferred to new localities neither can the relative levels of the earth's crusts above and beneath the waters vary from time to time as they are admitted to have varied at former periods as it will be demonstrated that they still do without the continents being in the course of ages modified and even entirely altered in their external configuration such events must clearly be accompanied by a complete change in the volume velocity and direction of the streams and land floods to which certain regions give passage that we should find therefore cliffs where the sea want committed ravages and from which it has now retired estuaries where hides hides once rose but which are now dried up valleys hallowed out by water where no streams now flow is no more than we should expect these and similar phenomena are the necessary consequences of physical causes now in operation and if there be no instability in the laws of nature similar fluctuations must recur again and again in time to come but however natural it may be that the force of running water in numerous valleys and of tides and currents in many tracts of the sea should now be spent it is by no means so easy to explain why the violence of the earthquake and the fire of the volcano should also have become locally extinct at successive periods we can look back to the time when the marine strata where on the great mass of etna rests had no existence and at the time is extremely modern in the earth's history this alone affords ground for anticipating that the eruptions of etna will one day cease nek guy surferis ardet for nakibus etna ignea semper elit neke en infuit ignea semper oved me down live 15 to 340 are the memorable words which are put into the mouth of pythagoras by the roman poet and they are followed by speculations as to the cause of volcanic vents shifting their positions whatever doubts the philosopher expresses as to the nature of these causes it is assumed as incontrovertible that the points of eruption will hereafter vary because they have formally done so a principle of reasoning which i have endeavored to show in former chapters has been too much set at nought by some of the earlier schools of geology which refuse to conclude that the great revolutions in the earth's surface are now in progress or that they will take place hereafter because they have often been repeated in former ages division of the subject volcanic action may be defined to be the influence exerted by the heated interior of the earth on its external covering if we adopt this definition without connecting it as humbolts has done with the theory of circular refrigeration or the cooling down of an original heated and fluid nucleus we may then class under a general head or the subterranean phenomena whether of volcanoes or earthquakes and those insensible movements of the land by which as will appear afterwards large districts may be depressed or elevated without convulsions according to this view i shall consider first the volcano secondly the earthquake thirdly the rising or sinking of the land in countries where there are no volcanoes or earthquakes fourthly the probable causes of the changes which result from subterranean agency it is a very general opinion that earthquakes and volcanoes have a common origin for both are confined to certain regions although the subterranean movements are least violent in the immediate proximity of volcanic vents especially where the discharge of area formed fluids and melted rock is made constantly from the same crater but as there are particular regions to which both points of the eruption and the movements of great earthquakes are confined i shall begin by tracing out the geographical boundaries of some of these that the reader may be aware of the magnificent scale on which the agency of subterranean fire is now simultaneously developed over the whole of the vast tracks alluded to active volcanic vents are distributed at intervals and most commonly arranged in a linear direction throughout the intermediate spaces there is often abundant evidence that the subterranean fire is at work continuously for the ground is convulsed from time to time by earthquakes gaseous vapours especially carbonic acid gas are disengaged plentifully from the soil springs often issue at very high temperature and their waters are usually impregnated with the same mineral matters as are discharged by volcanoes during eruptions volcanic regions region of the andes one of these great regions that of the andes of south america is one of the best defined extending from the southward of chili to the northward of keto from about latitude 43 degrees south to about two degrees north of the equator in this range however comprehending 45 degrees of latitude there is an alternation on a grand scale of districts of active with those of extinct volcanoes or which if not spent have at least been dormant for the last three centuries how long an interval of rest may entitle us to consider a volcano as entirely extinct is not easily determined but we know that in ishia there is intervened between two consecutive eruptions a pause of 17 centuries and the discovery of america is an event far too recent to date to allow us to even conjecture with the different portions of the andes nearly the whole of which are subject to earthquakes may not experience alternately a cessation and renewal of eruptions the first line of active vents which have been seen in eruption in the andes extends from latitude 43 degrees 28 minutes south or from yantalis opposite the isle of chilo it to coquimbo in latitude of 30 degrees south to these 13 degrees of latitude succeed more than eight degrees in which no recent volcanic eruptions have been observed we then come to the volcanoes of bolivia and peru reaching six degrees from south to north or from latitude 21 degrees south to last dude 15 degrees south between the peruvian volcanoes and those of keto another space intervenes of no less than 14 degrees of last dude said to be free from volcanic action so far as yet known the volcanoes of keto then succeed beginning about 100 geographical miles south of the equator and continuing for about 130 miles north of the line when then occurs another undisturbed interval of more than six degrees of latitude after which we arrive at the volcanoes of guatemala or central america north of the isthmus of panama having thus traced out the line from south to north i'm a first state in regard to the numerous events of chili that the volcanoes of yantalis and osorno were in eruption during the great earthquake of 1835 at the same moment that the land was shaken in chilo and in some parts of the chilean coast permanently upheaved whilst at one for an andes at the distance of no less than 720 geographical miles from yantalis an eruption took place beneath the sea some of the volcanoes of chili are of great height as that of the an tuco in latitude 37 degrees 40 minutes south the summit of which is at least 16 000 feet above the sea from the flanks of this volcano at a great height immense currents of lava have issued one of which flowed in the year 1828 this event is said to be an exception in the general rule few volcanoes in the andes and none of those in keto having been seen in modern times to pour out lava but having merely ejected vapor or scoriae both the basaltic or orbitic lathers and those of the felspathic class occur in chili and other parts of the andes but the volcanic rocks of the felspathic family are said by von bur to be generally not trachite but a rock which has been called anbisite or a mixture of augite and albite the last mentioned mineral contains soda instead of the potash formed in common felspath the volcano of ram kagwa latitude 34 degrees 15 minutes south is said to be always throwing out ashes and vapors like stromboli a proof of the permanently heated state of certain parts of the interior of the earth below a year rarely passes in chili without some slight shocks of earthquakes and in certain districts not a month those shocks which come from the side of the ocean are the most violent and the same is said to be the case in Peru the town of copiapo was laid waste by this terrible scourge in the years 1773 1796 and 1819 or in both cases after regular intervals of 23 years there have however been other shocks in that country in the periods intervening between the days above mentioned although probably all less severe at least on the exact same side of copiapo the evidence against a regular occurrence of volcanic convulsions at state and periods is so strong as a general fact that we must be on our guard against attaching too much importance to a few striking with probably accidental coincidences among these last might be reduced the case of lima violently shaken by an earthquake on the 17th of june 1578 and again on the very same day 1678 or the eruptions of coseguina in the years 1709 and 1809 which are the only two recorded of that volcano previous to that of 1835 of the permanent upheaval of land after earthquakes in chili i shall have occasion to speak in the next chapter where it will also be seen that great shocks often coincide with eruptions either submarine or from the cones of the andes showing the identity of the force which elevates continents with that which causes volcanic outbursts the space between chili and peru in which no volcanic action has been observed is 160 nautical leagues from south to north it is however as von burr observes that part of the andes which is least known being thinly peopled and in some parts entirely desert the volcanoes of peru rise from a lofty platform to vast heights above the level of the sea from 17 000 to 20 000 feet the lava which has issued from viejo latitudes 16 degrees 55 minutes south accompanied by a pumice is composed of a mixture of crystals of albitic feldspar whore and blend and mica a rock which has been considered as one of the varieties of andesite some tremendous earthquakes which have visited peru in modern times will be mentioned in a subsequent chapter the volcanoes of quito occurring between the second degree of south and the third degree of north latitude rise to vast elevations above the sea many of them being between 14 000 and 18 000 feet high the indians of liqar have a tradition that the mountain core laltar or kapak urku which means the chief was once the highest of those near the equator being higher than chimborazo but in the rain of weenia abomata before the discovery of america a prodigious eruption took place which lasted eight years and broke it down the fragments of track height says monsieur musango which once formed the conical summit of the celebrated mountain are at this day spread over the plain kotopaxi is the most lofty of all the south african volcanoes which have been in the in a state of activity in modern times its height being 18 858 feet and its eruptions have been more frequent and destructive than those of any other mountain it is a perfect cone usually covered with an enormous bed of snow which has however been sometimes melted suddenly during an eruption as in january 1803 for example when the snows were dissolved in one night deluges are often caught in the andes by the libru faction of great masses of snow and sometimes by the rending open during earthquakes of subterranean cavities filled with water in these inundations fine volcanic sand loose stones and other materials with the water with in its descent are swept away and a vast quantity of mud called moya is thus formed and carried down into the lower regions mud derived from the source descended in 1797 from the sides of tunguagua in quito and filled valleys a thousand feet wide to the depth of 600 feet damming up rivers and causing lakes in these currents and lakes of moya thousands of small fish are sometimes enveloped which according to humboldt have lived and multiplied in subterranean cavities there are a great quantity of these fish were ejected from the volcano of imabudo in 1691 that fevers with prevailed at the period were attributed to the effluvia arising from the putrid animal matter in quito many important revolutions in the physical features of the country are said to have resulted within the within the memory of man from the earthquakes by which it has been convulsed monsieur boussango declares his belief that if a full register had been kept of all the convulsions experienced here and in other populous districts of the andes it would be found that the trembling of the earth had been incessant the frequency of the movement he thinks is not due to volcanic explosions but to the continual falling in of masses of rock which have been fractured and upheaved in solid form at a comparatively recent epoch but a longer series of observations will be requisite to confirm this opinion according to the same author the height of several mountains of the andes has diminished in modern times the great crests of cordiella of the andes is depressed at the ismouth of palomar to a height of about 1000 feet and at the lowest point of separation between the two seas near the Gulf of san miguel to 150 feet what some geographers regard as a continuation of that chain in central america lies to the east of a series of volcanoes many of which are active in the provinces of pastore pro bayan and guatemala coseguina on the south side of the Gulf of fornesca was the interruption in january 1835 and some of its ashes fell out to truxedio on the shores of the gulf of mexico what is still more rebargable on the same day at kingston in jamaica the same shower of ashes fell having been carried by an upper countercurrent against the regular east wind which was then blowing kingston is about 700 miles distant from coseguina and these ashes must have been more than four days in the air having traveled 170 miles a day eight leagues to the southward of the crater the ashes cover the ground the depth of three yards and a half destroying the woods and dwellings thousands of cattle perished the bodies being in many instances one mass of scorched flesh deer and other wild animals sought the towns for protection many birds and quadrupeds were found suffocated in the ashes and the neighboring streams were strewed with dead fish such facts threw light on geological monuments for in the ashes thrown out at remote periods from the volcanoes of orverna now extinct we find the bones and skeletons of lost species of quadrupeds mexico the great volcanic chain after having thus pursued its course for several thousand miles from south to north sends off a branch in a new direction in mexico in the parallel of the city of that name and it's prolonged in a great platform between the 18th and 22nd degrees of north latitude five active volcanoes transverse mexico from west to east orizaba poco cattopel rolulio and colima rolulio which is in the center of the great platform is no less than 120 miles from the nearest ocean an important circumstance are showing that the proximity of the sea is not a necessary condition although certainly a very general characteristic of the position of active volcanoes the extraordinary eruption of this mountain in 1759 will be described in the sequel if the line which connects these five vents be prolonged in a westerly direction it cuts the volcanic group of islands called the aisles are revealed here to the north of mexico there are said to be three or according to some five volcanoes in the peninsula of california and a volcano was reported to have been in eruption in the northwest coast of america near the columbia river latitude 45 degrees 37 minutes north west indies to return to the andes of keto van boek inclines that to the belief that if we were better acquainted with the region to the east of madalena and with new garanda and the caracas we might find the volcanic chain of the andes to be connected with that of the west indian or carabi island the truth of this conjecture has almost been set at rest by the eruption in 1848 of the volcano of zamba in new granada at the mouth of the river madalena of the west indian islands there are two parallel series the one to the west which are all volcanic and which rise to the height of several thousand feet the others to the east for the most part composed of calcareous rocks and very low in the former or volcanic series are granada saint vincent saint lucia martinik dominica guadalupe monseads nivis and saint ustas in the calcareous chain otabago barbados marigalante grande terre destegare antigua barbadua saint bartholomew and saint martin the most considerable eruptions in modern times have been those of saint vincent great earthquakes have agitated saint dominica as will be seen the 29th chapter i have before mentioned page 270 the violent earthquake which in 1812 convulsed the valley of mississippi at new madrid for the space of 300 miles in length of which more will be said in the 27th chapter this happened exactly at the same time as the great earthquake of caracas so that it is possible that these two points are part of one subterranean volcanic region the island of jamaica with a tract of the contiguous sea has often experienced tremendous shocks and these are frequent along the line extending from jamaica to san dominico and portorico thus it will be seen that without taking account of the west indian and mexican branches a linear train of volcanoes and tracts shaken by earthquakes may be traced from the island of chiloé and opposite coast to mexico or even perhaps to the mouth of the columbian river a distance upon the hole as great from the pole to the equator in regards to the western limits of the region they lie deep beneath the waves of the pacific and must continue unknown to us on the east they are not prolonged except where they include the west indian islands to a great distance for there seems to be no indications of volcanic disturbances in Buenos Aires brazil and the united states of north america end of chapter 22 part 1 recording by melchior raywood