 CHAPTER XII CONSOLIDATION OF FOSSILIFERUS STRATA Some deposits originally solid, transition and slaty texture, crystalline character of plutonic and metamorphic rocks, theory of their origin, essentially subterranean, no proofs that they were produced more abundantly at remote periods. Another argument in favor of the dissimilarity of the causes operating at remote and recent eras has been derived by many geologists from the more compact stony and crystalline texture of the older as compared with the newer rocks. CONSOLIDATION OF STRATA This subject may be considered first in reference to the fossiliferous strata, and secondly in reference to those crystalline and stratified rocks which contain no organic remains, such as nice and mycoshist. There can be no doubt that the former of these classes, or the fossiliferous, are generally more compact and stony in proportion as they are more ancient. It is also certain that a great part of them were originally in a soft and incoherent state, and that they have been since consolidated. Thus we find occasionally that shingle and sand have been agglutinated firmly together by a furuganus or siliceous cement, or that liman solution has been introduced, so as to bind together materials previously incoherent. Organic remains have sometimes suffered a singular transformation, as for example, where shells, corals, and wood are solicified, their calcareous or lignious matter having been replaced by nearly pure silica. The constituents of some beds have probably set and become hard for the first time when they emerged from beneath the water, but on the other hand we observe in certain formations, now in progress, particularly in coral reefs and in deposits from the waters of mineral springs, both calcareous and siliceous that the texture of rocks may sometimes be stony from the first. This circumstance may account for exceptions to the general rule, not unfrequently met with, where solid strata are superimposed on others of a plastic and incoherent nature, as in the neighborhood of Paris where the tertiary formations, consisting often of compact limestone and siliceous grit, are more stony than the subjacent chalk. It will be readily understood that the various solidifying causes, including those above enumerated, together with the pressure of incumbent rocks and the influence of subterranean heat, most all of them require time in order to exert their full power. If in the course of ages they modify the aspect and internal structure of stratified deposits, they will give rise to a general distinctness of character in the older, as contrasted with the newer formations. But this distinctness will not be the consequence of any original diversity. They will be unlike, just as the wood in the older trees of a forest usually differs in texture and hardness from that of younger individuals of the same species. TRANSITION TEXTURE In the original classification of Werner, the highly crystalline rocks, such as granite and nice, which contain no organic remains, were called a primary, and the fossiliferous strata secondary. While to another class of an age intermediate between the primary and the secondary, he gave the name of TRANSITION. They were termed TRANSITION because they partook, in some degree, in their mineral composition of the nature of the most crystalline rocks, such as nice and mycosis, while they resembled the fossiliferous series in containing occasionally organic remains and exhibiting evident signs of a mechanical origin. It was at first imagined that the rocks having this intermediate texture had been all deposited subsequently to the series called primary, and before all the more earthy and fossiliferous formations. But when the relative position and organic remains of these TRANSITION rocks were better understood, it was perceived that they did not all belong to one period. On the contrary, the same mineral characters were found in strata of very different ages and some formations occurring in the Alps, which several of the ablest scholars of Werner had determined to be TRANSITION, were ultimately ascertained by means of their fossil contents and position, to be members of the Cretaceous and even of the Numeolithic or Eocene period. These strata had in fact acquired the TRANSITION texture from the Influence of Causes which since their deposition had modified their internal arrangement. Another and origin of Plutonic and Metamorphic rocks, among the most singular of the changes super-induced on rocks, we have occasionally to include the slaty texture, the divisional planes of which sometimes intersect the TRUE planes of stratification and even pass directly through embedded fossils. If then the crystalline, the slaty, and other modes of arrangement, once deemed characteristic of certain periods in the history of the earth, have in reality been assumed by fossiliferous rocks of different ages and at different times, we are prepared to enquire whether the same may not be true of the most highly crystalline state, such as that of NICE, like a Schist and Statuary marble, that the peculiar characteristics of such rocks are really due to a variety of modifying causes, has long been suspected by many geologists, and the doctrine has gained ground of late, although a considerable difference of opinion still prevails. According to the original Neptunian theory, all the crystalline formations were precipitated from a universal menstruum, or chaotic fluid, antecedently to the creation of animals and plants, the unstratified granite having been first thrown down was to serve as a floor or foundation on which NICE and other stratified rocks might repose. Afterwards, when the igneous origin of granite was no longer disputed, many conceived that a thermal ocean enveloped a globe, at a time when the first formed crust of granite was cooling, but when it still retained much of its heat. The hot waters of this ocean held in solution the ingredients of NICE, like a Schist, horn blend Schist, clay slate and marble, rocks which were precipitated, one after the other in a crystalline form. No fossils could be enclosed in them, the high temperature of the fluid and the quantity of mineral matter which it held in solution rendering it unfit for the support of organic beings. It would be inconsistent with the plan of this work, to enter here into a detailed account of what I have elsewhere termed the metamorphic theory, but I may state that it is now demonstrable in some countries that fossiliferous formations, some of them of the age of the Silurian strata, as near Christiana in Norway, others belonging to the Olytic period as around Currara and Italy, have been converted partially into NICE, like a Schist and statuary marble. The transmutation has been effected apparently by the influence of subterranean heat, acting under great pressure, or by chemical and electrical causes operating in a manner not yet understood, and which have been termed plutonic action, as expressing, in one word, all the modifying causes which may be brought into play at great depths, and under conditions never exemplified at the surface. To this plutonic action, the fusion of granite itself and the bowels of the earth, as well as the super inducement of the metamorphic texture into sedimentary strata, must be attributed. And in accordance with these views, the age of each metamorphic formation may be said to be twofold, for we have first to consider the period when it originated, an aqueous deposit, in the form of mud, sand, marble, or limestone, secondly the date at which it acquired the crystalline texture. The same strata, therefore, may according to this view, be very ancient in reference to the time of their deposition, and very modern in regard to the period of their assuming the metamorphic character. No proofs that these crystalline rocks were produced more abundantly at remote periods. Several modern writers, without denying the truth of the plutonic or metamorphic theory, still contend that the crystalline and non-fossiliferous formations, whether stratified or unstratified, such as nice and granite, are essentially ancient as a class of rocks. They were generated, say, they, most abundantly in the primeval state of the globe, since which time the quantity produced has been always on the decrease, until it became very inconsiderable in the olytic and cretaceous periods, and quite effervescent before the commencement of the tertiary epoch. Now the justness of these views depends almost entirely on the question whether granite, nice, and other rocks of the same order ever originated at the surface, or whether according to the opinions above adopted, they are essentially subterranean in their origin, and therefore entitled to the appellation of hypogeum. If they were formed superficially in their present state, and as copiously in the modern as in the more ancient periods, we ought to see a greater abundance of tertiary and secondary than of primary granite and nice. But if we adopt the hypogeum theory before explain their rapid diminution in volume among the visible rocks in the Earth's crust in proportion, as we investigate the formations of a newer date, is quite intelligible. If a melted mass of matter be now cooling very slowly, at the depth of several miles beneath the crater of an active volcano, it must remain invisible until great revolutions in the Earth's crust have been brought about. So also if stratified rocks have been subjected to plutonic action, and after having been baked or reduced to semi-fusion, are now cooling and crystallizing far underground, it will probably require the lapse of many periods before they will be forced up to the surface and exposed to view, even at a single point. To effect this purpose, there may be need of as great a development of subterranean movement, as that which in the Alps, Andes, and Himalaya has raised marine strata containing ammonites to the height of 8,000, 14,000, and 16,000 feet. By parity of reasoning, we can hardly expect that any hypogeum rocks of the tertiary periods will have been brought within the reach of human observation, seeing that the emergence of such rocks must always be so long posterior to the date of their origin, and still less conformations of this class become generally visible until so much time has elapsed as to confer on them a high relative antiquity. Extensive denudation must also combine with upheaval, before they can be displayed at the surface throughout wide areas. Volgeologists, who reflect on subterranean movements now going on, and the eruptions of active volcanoes, are convinced that great changes are now continually in progress in the interior of the Earth's crust far out of sight. They must be conscious therefore that the inaccessibility of the regions in which these alterations are taking place compels them to remain in ignorance of a great part of the working of existing causes, so that they can only form vague conjectures in regard to the nature of the products, which volcanic heat may elaborate under great pressure. But when they find in mountain chains of high antiquity that what was once the interior of the Earth's crust has since been forced outwards and exposed to view they will naturally expect in the examination of those mountainous regions to have an opportunity of gratifying their curiosity by obtaining a sight not only of the superficial strata of remote eras, but also of the contemporaneous nether-formed rocks. Having recognized therefore in such mountain chains some ancient rocks of aqueous and volcanic origin corresponding in character to superficial formations of modern date they will regard any other class of ancient rocks such as granite and nice as the residual phenomena of which they are in search. These latter rocks will not answer the expectations previously formed of their probable nature and texture, unless they were a foreign and mysterious aspect and have in some places been fused or altered by subterranean heat, in a word unless they differ wholly from the fossiliferous strata deposited at the surface or from the lava and scourier thrown out by volcanoes in the open air. It is the total distinctness therefore of crystalline formations such as granite, hornblend, schist, and the rest, from every substance of which the origin is familiar to us, and constitutes their claim to be regarded as the effects of causes now in action in the subterranean regions. They belong not to an order of things which has passed away. They are not the monuments of a primeval period bearing inscribed upon them in obsolete characters the words and phrases of a dead language, but they teach us that part of the living language of nature which we cannot learn by our daily intercourse with what passes on the habitable surface. End of Chapter 12. Chapter 13 Part 1 of Principles of Geology. This is a LibriVox recording. While LibriVox recordings are in the public domain, for more information or to volunteer please visit LibriVox.org. Principles of Geology by Charles Lyle. Chapter 13 Part 1. Uniformity in the series of past changes in the animate and inanimate world. Supposed alternate periods of repose and disorder. Observed facts in which this doctrine has originated. These may be explained by supposing a uniform and uninterrupted series of changes. Threefold consideration of this subject. First in reference to the living creation, extinction of species and origin of new animals and plants. Secondly, in reference to the changes produced in the Earth's crust by the continuance of subterranean movements in certain areas. And their transference after long periods to new areas. Thirdly, in reference to the laws which govern the formation of fossiliferous strata. And the shifting of the areas of sedimentary deposition. On the combined influence of all these modes and causes of change. In producing breaks and chasms in the chain of records. Making remarks on the identity of the ancient and present system of terrestrial changes. Origin of the doctrine of alternate periods of repose and disorder. It has been truly observed that when we arrange the fossiliferous formations in chronological order. They constitute a broken and defective series of monuments. We pass without any intermediate gradations from systems of strata which are horizontal. To other systems which are highly inclined. From rocks of peculiar mineral composition. To others which have a character wholly distinct. From one assemblage of organic remains to another. In which frequently all the species and most of the genera are different. These violations of continuity are so common as to constitute the rule rather than the exception. And they have been considered by many geologists as conclusive in favor of sudden revolutions in the inanimate and animate world. According to speculations of some writers. There have been in the past history of the planet alternate periods of tranquility and convulsion. The former enduring for ages and resembling that state of things now experienced by man. The other brief transient and paroxysmal giving rise to new mountains seas and valleys annihilating one set of organic beings and ushering in the creation of another. It will be the object of the present chapter to demonstrate that these theoretical views are not borne out by a fair interpretation of geological monuments. It is true that in the solid framework of the globe we have a chronological chain of natural records that many links in this chain are wanting. But a careful consideration of all the phenomena will lead to the opinion that the series was originally defective. That it has been rendered still more so by time. And a great part of what remains is inaccessible to man, and even of that fraction which is accessible nine-tenths are to this day unexplored. How the facts may be explained by assuming a uniform series of changes. The readiest way perhaps of persuading the reader that we may dispense with great and sudden revolutions in the geological order of events is by showing him how a regular and uninterrupted series of changes in the animate and inanimate world may give rise to such breaks in the sequence. And such unconformability of stratified rocks are as usually thought to imply convulsions and catastrophes. It is scarcely necessary to state that the order of events thus assumed to occur, for the sake of illustration, must be in harmony with all the conclusions legitimately drawn by geologists from the structure of the earth, and must be equally in accordance with the changes observed by man to be now going on in the living as well as in the inorganic creation. It may be necessary in the present state of science to supply some part of the assumed course of nature hypothetically, but if so, this must be done without any violation of probability, and always consistently with the analogy of what is known both of the past and present economy of our system. Although the discussion of so comprehensive a subject must carry the beginner far beyond his depth, it will also, it is hoped, stimulate his curiosity, and prepare him to read some elementary treatise on geology with advantage, and teach him the bearing on that science of the changes now in progress on the earth. At the same time it may enable him the better to understand the intimate connection between the second and third books of this work, the former of which is occupied with the changes in the inorganic, the latter with those of the organic creation. In pursuance, then, of the plan above proposed, I shall consider in this chapter, first, what may be the course of fluctuation in the animate world, secondly, the mode in which contemporaneous subterranean movements affect the earth's crust, and thirdly, the laws which regulate the deposition of sediment. The concept of change considered first, in reference to the living creation. First in regard to the vicissitudes of the living creation, all are agreed that the sedimentary strata found in the earth's crust are divisible into a variety of groups, more or less dissimilar in their organic remains and mineral composition, the conclusion universally drawn from the study, and comparison of these fossiliferous groups is this, that at successive periods distinct tribes of animals and plants have inhabited the land and waters, and that the organic types of the newer formations are more analogous to species now existing than those of more ancient rocks. If we then turn to the present state of the animate creation and inquire whether it has now become fixed and stationary, we discover that, on the contrary, is in a state of continual flux that there are many causes in action which tend to the extinction of species, and which are conclusive against the doctrine of their unlimited durability. That natural history has been successfully cultivated for so short a period that a few examples only of local, and perhaps but one or two of absolute, extirpation can as yet be proved, and these only where the interference of man has become conspicuous. It will nevertheless appear evident from the facts and arguments detailed in the third book, from the 37th to the 42nd chapters, inclusive, that man is not the only exterminating agent, and that independently of his intervention the annihilation of species is promoted by the multiplication and gradual diffusion of every animal or plant. It will also appear that every alteration in the physical geography and climate of the globe cannot fail to have the same tendency. If we proceed still farther and inquire whether new species are substituted from time to time for those which die out, and whether there are certain laws appointed by the author of nature to regulate such new creations, we find that the period of human observation is as yet too short to afford data for determining so weighty a question. All that can be done is to show that the successive introduction of new species may be a constant part of the economy of the terrestrial system, without our having any right to expect that we should be in possession of direct proof of the fact. The appearance again and again of new species may easily have escaped detection, since the numbers of known animals and plants have augmented so rapidly within the memory of persons now living, as to have doubled in some classes, and quadrupled in others. It will also be remarked in the sequel, book 3, chapter 43, that it must always be more easy if species proceeded originally from single stocks to prove that one which formerly abounded in a given district has seized to be, than that another has been called into being for the first time. If therefore there be as yet only one or two unequivocable instances of extinction, namely those of the dodo and solitaire, it is scarcely reasonable as yet to hope that we should be cognizant of a single instance of the first appearance of a new species, recent origin of man, and gradual approach in the tertiary fossils of successive periods from an extinct to the recent fauna. The geologist, however, if required to advance some fact, which may lend countenance to the opinion that in the most modern times, that is to say after the greater part of the existing fauna and flora were established on the earth, there has still been a new species super-added, may point to man himself as furnishing the required illustration. For a man must be regarded by the geologist as a creature of yesterday, not merely in reference to the past history of the organic world, but also in relation to that particular state of the animate creation of which he forms a part. The comparatively modern introduction of the human race is proved by the absence of the remains of man and his works, not only from all strata containing a certain proportion of fossil shells of extinct species, but even from a large part of the newest strata, in which all the fossil individuals are referable to species still living. To enable the reader to appreciate the full force of this evidence, I shall give a slight sketch of the information obtained from the newest strata, respecting fluctuations in the animate world, in times immediately antecedent to the appearance of man, in tracing the series of fossiliferous formations from the more ancient to the more modern, the first deposits in which we meet with assemblages of organic remains, having a near analogy to the fauna of certain parts of the globe in our own time, are those commonly called tertiary. Even in the Eocene, or oldest subdivision of these tertiary formations, some few of the Testasia belong to existing species, although almost all of them, and apparently all the associated vertebrata are now extinct. These Eocene strata are succeeded by a great number of more modern deposits, which depart gradually in the character of their fossils from the Eocene type, and approach more and more to that of the living creation. In the present state of science, it is chiefly by the aid of shells that we are enabled to arrive at these results, for all classes the Testasia are the most generally diffused in a fossil state, and may be called the metals principally employed by nature in recording the chronology of past events. In the Myocene deposits, which are next in succession to the Eocene, we begin to find a considerable number, although still a minority, of recent species intermixed with some fossils common to the preceding epic. We then arrive at the Pliocene strata, in which species now contemporary with man begin to preponderate, and in the newest of which nine-tenths of the fossils agree with species still inhabiting the neighboring sea. In this passing, from the older to the newer members of the tertiary system, we meet with many chasms, but none which separate entirely by a broad line of demarcation, one state of the organic world from another. There are no signs of an abrupt termination of one fauna and flora, and the starting into life of new and wholly distinct forms. Although we are far from being able to demonstrate geologically an insensible transition from the Eocene to the Myocene, or even from the latter to the recent fauna, yet the more we enlarge and perfect our general survey, the more nearly do we approximate to such a continuous series, and the more gradually we are conducted from times when many of the genera and nearly all the species were extinct to those in which scarcely a single species flourished, which we do not know to exist at present. Dr. A. Filippi, indeed, after an elaborate comparison of the fossil tertiary shells of Sicily, with those now living in the Mediterranean, announces as the result of his examination that there are strata in that island which attest a very gradual passage from a period, when only thirteen and a hundred of the shells were like the species now living in the sea, to an era when the recent species had attained a proportion of ninety-five and a hundred. There is therefore evidence, he says, in Sicily of this revolution in the animate world having been effected. Without the intervention of any convulsion or abrupt changes, certain species having from time to time died out, and others having been introduced, until at length the existing fauna was elaborated. It had often been objected that the evidence of fossil species occurring in two consecutive formations was confined to the testatia or zoophytes, the characters of which are less marked and decisive than those afforded by the vertebrate animals. But Mr. Owen has lately insisted on the important fact that not a few of the quadrupeds which now inhabit our island, and among others the horse, the ass, the hog, the smaller wild ox, the goat, the red deer, the roe, the beaver, and many of the diminutive rodents, are the same as those which once co-existed with the mammoth, the great northern hippopotamus, two kinds of rhinoceros, and other mammalia long since extinct. A part, he observes, and not the whole of the modern tertiary fauna has perished, and hence we may conclude that the cause of their destruction has not been a violent and universal catastrophe from which none could escape. Had we discovered evidence that man had come into the earth at a period as early as that when a large number of the fossil quadrupeds now living, and almost all the recent species of the land, freshwater, and marine shells were in existence, we should have been compelled to ascribe a much higher antiquity to our species, than even the boldest speculations of the ethnologist require, for no small part of the great physical revolution depicted on the map of Europe, Plate III, before described, took place very gradually, after the recent testacea abounded almost to the exclusion of the extinct. Thus, for example, in the deposits called the Northern Drift, or the glacial formation of Europe in North America, the fossil marine shells can easily be identified with species either now inhabiting the neighboring sea or living in the seas of higher latitudes. Yet they exhibit no memorials of the human race or of articles fabricated by the hand of man. Some of the newest of these strata, passing by the name of raised beaches, occur at moderate elevations on the coast of England, Scotland, and Ireland. Other examples are met with on a more extended scale in Scandinavia, as at the height of 200 feet at Udavala in Sweden, and at twice the elevation near Christiana in Norway, also at an attitude of six or seven hundred feet in places further north, they consist of beds of sand and clay, filling hollows in a district of granite and gnice, and they must closely resemble the accumulations of Shelley matter, now in progress at the bottom of the Norwegian fjords. The rate at which the land is now rising in Scandinavia is far too irregular in different places to afford a safe standard for estimating the minimum of time required for the upheaval of the fundamental granite and its marine Shelley covering to the height of so many hundred feet, but according to the greatest average of five or six feet in a century, the period required would be very considerable and nearly the whole of it, as well as the antecedent epoch of submergence, seems to have preceded the introduction of man into these parts of the earth. There are other post-tertiary formations of fluviatile origin in the center of Europe, in which the absence of human remains is perhaps still more striking, because when formed they must have been surrounded by dry land. I allude to the silt, or loess, of the basin of the Rhine, which must have gradually filled up the great valley of that river, since the time when its waters and the contiguous lands were inhabited by the existing species of freshwater and terrestrial mollusks. Showers of ashes thrown out by some of the last eruptions of the Eiffel volcanoes fell during the deposition of the fluviatile silt and were inter-stratified with it, but these volcanoes became exhausted. The valley was re-excavated through the silt, and again reduced to its present form before the period of human history. The study, therefore, of this Shelley silt reveals to us the history of a long series of events which occurred after the Testatia now living inhabited the land and rivers of Europe, and the whole terminated without any signs of the coming of man into that part of the globe. To cite a still more remarkable example, we observe in Sicily, a lofty table-and and hills sometimes rising to the height of 3,000 feet, capped with a limestone, in which from 70 to 85% of the fossil Testatia are specifically identical with those now inhabiting the Mediterranean. These calcareous and other argillatious strata of the same age are intersected by deep valleys which have been gradually formed by denudation, but have not varied materially in width or depth since Sicily was first colonized by the Greeks. The limestone, moreover, which is of so late a date in geological chronology, was quarried for building those ancient temples of Ghirgenti and Syracuse, of which the ruins carry us back to a remote era in human history. If we are lost in conjectures when speculating on the ages required to lift up these formations to the height of several thousand feet above the sea, how much more remote must be the era when the same rocks were gradually formed beneath the waters? To conclude, it appears that in going back from the recent to the Eocene period, we are carried by many successive steps from La Fonna, now contemporary with man, to an assemblage of fossil species wholly different from those now living. In this retrospect, we have not yet succeeded in tracing back a perfect transition from the recent to the extinct fauna. But there are usually so many species in common to the groups which stand next in succession as to show that there is no great chasm, no signs of a crisis when one class of organic beings were annihilated to give place suddenly to another. This analogy, therefore, derived from a period of the Earth's history, which can be best compared with the present state of things, and more thoroughly investigated than any other, leads to the conclusion that the extinction and creation of species has been and is the result of a slow and gradual change in the organic world. Chapter 13, Part 2 of Principles of Geology. This is LibriVox Recording. While LibriVox recordings are in the public domain, for more information or to volunteer, please visit LibriVox.org. Principles of Geology by Charles Lyle. Chapter 13, Part 2. To pass on to another of the three topics before proposed for discussion, the reader will find in the account given in the second book of the earthquakes recorded in history that certain countries have from time immemorial been rudely shaken again and again while others, comprising by far the largest part of the globe, have remained to all appearance motionless. In the regions of convulsion, rocks have been rent asunder, the surface has been forced up into ridges, chasms have opened, or the ground throughout large spaces has been permanently lifted up above or let down below its former level. In the regions of tranquility some areas have remained at rest, but others have been ascertained by a comparison of measurements, made at different periods, to have risen by an insensible motion as in Sweden, or to have subsided very slowly as in Greenland, that these same movements, whether ascending or descending, have continued for ages in the same direction, has been established by geological evidence. Thus we find both on the east and west coast of Sweden, that ground which formerly constituted the bottom of the Baltic and of the ocean, has been lifted up to an elevation of several hundred feet above high water mark. The rise within the historical period has not amounted to many yards, but the greater extent of antecedent upheaval is proved by the occurrence in inland spots several hundred feet high, of deposits filled with fossil shells of species now living either in the ocean or the Baltic. To detect proofs of slow and gradual subsidence must in general be more difficult, but the theory which accounts for the form of circular coral reefs and lagoon islands, and which will be explained in the last chapter of the third book, will satisfy the reader that there are spaces on the globe several thousand miles in circumference, throughout which the downward movement has predominated for ages, and yet the land has never in a single instance gone down suddenly for several hundred feet at once. Yet geology demonstrates that the persistency of subterranean movements in one direction has not been perpetual throughout all past time. There have been great oscillations of level by which a surface of dry land has been submerged to a depth of several thousand feet, and then at a period long subsequent raised again and made to emerge. Nor have the regions now motionless been always at rest, and some of those which are at present the theatres of reiterated earthquakes have formerly enjoyed a long continuance of tranquility. But although disturbances have seized after having long prevailed, or have recommended after a suspension for ages, there has been no universal disruption of the earth's crust or desolation of the surface since times the most remote. The non-occurrence of such a general convulsion is proved by the perfect horizontally, now retained by some of the most ancient fossiliferous strata throughout wide areas. Inferences derived from Unconformable Strata. That the subterranean forces have visited different parts of the globe at successive periods, is inferred chiefly from the unconformability of strata belonging to groups of different ages. Thus, for example, on the border of Wales and Shropshire, we find the slaty beds of the ancient Solurian system curved and vertical, while the beds of the overlying carboniferous shale and sandstone are horizontal. All are agreed that in such a case the older set of strata had suffered great dislocation before the deposition of the newer or carboniferous beds, and that these last have never since been convolved by any movements of excessive violence. But the strata of the inferior group suffered only a local derangement, and rocks of the same age are by no means found everywhere in a curved or vertical position. In various parts of Europe, and particularly near Lake Vaner in the south of Sweden, and in many parts of Russia, beds of the same Solurian system maintain the most perfect horizontality, and a similar observation may be made respecting limestones and shales of the Lake Antiquity in the Great Lake District of Canada and the United States. They are still as flat and horizontal as when first formed, yet since their origin, not only have most of the actual mountain chains been uplifted, but the very rocks of which those mountains are composed have been formed. It would be easy to multiply instances of similar unconformability in formations of other ages, but a few more will suffice. The coal measures before alluded to as horizontal on the borders of Wales are vertical in the Mende Pils in Somersetshire, where the overlying beds of the new red sandstone are horizontal. Again in the worlds of Yorkshire, the last mentioned sandstone supports on its curved and inclined beds the horizontal chalk. The chalk again is vertical on the flanks of the Pyrenees and the tertiary strata repose unconformably upon it. Consistency of local disturbances with general uniformity. As almost every country supplies illustrations of the same phenomena, they who advocate the doctrine of altered periods of disorder and repose may appeal to the facts above described, as proving that every district has been by turns convulsed by earthquakes and then respited for ages from convulsions. But so it might with equal truth be affirmed that every part of Europe has been visited alternately by winter and summer, although it has always been winter and always summer in some part of the planet, and neither of these seasons has ever rained simultaneously over the entire globe. They have been always shifting about from place to place, but the vicissitudes which recur thus annually in a single spot are never allowed to interfere with the invariable uniformity of seasons throughout the whole planet. So in regard to subterranean movements, the theory of the perpetual uniformity of the force which they exert on the Earth's crust is quite consistent with the admission of their alternate development and suspension for indefinite periods within limited geographical areas. Uniformity of change considered thirdly in reference to sedimentary deposition. It now remains to speak of the laws governing the deposition of Neustratta. If we survey the surface of the globe, we immediately perceive that it is divisible into areas of deposition and non-deposition. Or in other words, at any given time, there are spaces which are the recipients, others which are not the recipients of sedimentary matter. No Neustratta, for example, are thrown down on dry land, which remains the same from year to year, whereas in many parts of the bottom of seas and lakes, mud sand and pebbles are annually spread out by rivers and currents. There are also great masses of limestone growing in some seas, or in mid-ocean chiefly composed of corals and shells. No sediment deposited on dry land. As to the dry land, so far from being the receptacle of fresh ascensions of matter, it is exposed almost everywhere to waste away. Forests may be as dense and lofty as those of Brazil, and may swarm with quadrupeds, birds and insects. Yet, at the end of ten thousand years, one layer of black mold, a few inches thick, may be the sole representative of those myriads of trees, leaves, flowers and fruits, those innumerable bones and skeletons of birds, quadrupeds and reptiles, which tenanted the fertile region. Should this land be at length submerged, the waves of the sea may wash away in a few hours the scanty covering of mold, and it may merely impart a darker shade of color to the next stratum of moral sand, where other matter newly thrown down. So also, at the bottom of the ocean, where no sediment is accumulating, seaweed zoo-o-fights, fish and even shells may multiply for ages and decompose, leaving no vestige of their form or substance behind. Their decay in water, although more slow, is as certain and eventually as complete as in the open air. Nor can they be perpetuated for indefinite periods in a fossil state, unless embedded in some matrix which is impervious to water, or which at least does not allow a free percolation of that fluid impregnated, as it usually is, with a slight quantity of carbonic or other acid. Such a free percolation may be prevented either by the mineral nature of the matrix itself, or by the superposition of an impermeable stratum. But if unimpeded, the fossil shell or bone will be dissolved and removed particle after particle, and thus entirely effaced, unless petrofaction or the substitution of mineral for organic matter happened to take place, that there has been land as well as sea at all former geological periods. We know from the fact that fossil trees and terrestrial plants are embedded in rocks of every age. Occasionally lacustrine and fluviatile shells, insects, or the bones of amphibious or land reptiles point to the same conclusion. The existence of dry land, at all periods of the past, implies as before mentioned the partial deposition of sediment or its limitation to certain areas, and the next point to which I shall call the reader's attention is the shifting of these areas from one region to another. First then, variations in the site of sedimentary deposition are brought about independently of subterranean movements. There is always a slight change from year to year or from century to century. The sediment of the Rhone, for example, thrown into the lake of Geneva, is now conveyed to a spot a mile and a half distant from that where it accumulated in the 10th century, and six miles from the point where the delta began originally to form. We may look forward to the period when this lake will be filled up and then the distribution of the transported matter will be suddenly altered for the mud and sand brought down from the Alps will thence forth instead of being deposited near Geneva be carried nearly 200 miles southward, where the Rhone enters the Mediterranean. In the deltas of large rivers, such as those of the Ganges and Indus, the mud is first carried down for many centuries through one arm, and on this being stopped up, it is discharged by another, and may then enter the sea at a point 50 or 100 miles distance from its first receptacle. The direction of marine currents is also liable to be changed by various accidents, as by the heaping up of new sandbanks or the weering away of cliffs and promontories. But secondly, all these causes of fluctuation in the sedimentary areas are entirely subordinate to those great upward or downward movements of land which have been already described as prevailing over large tracts of a globe. By such elevation or subsidence, certain spaces are gradually submerged or made gradually to emerge. In the one case, sedimentary deposition may be suddenly renewed after having been suspended for ages, in the other as suddenly made to cease after having continued for an indefinite period. Causes of variation in mineral character of successive sedimentary groups. If deposition be renewed after a long interval, the new strata will usually differ greatly from the sedimentary rocks previously formed in the same place, and especially if the older rocks have suffered derangement, which implies a change in the physical geography of the district since the previous conveyance of sediment to the same spot. It may happen, however, that even when the inferior group is horizontal and conformable to the upper strata, these last may still differ entirely in mineral character because since the origin of the older formation, the geography of some distant country has been altered. In that country, rocks before concealed may have become exposed by denudation. Volcanoes may have burst out and covered the surface with scourier and lava, or new lakes may have been formed by subsidence, and other fluctuations may have occurred by which the materials brought down from vents by rivers to the sea have acquired a distinct mineral character. It is well known that the stream of the Mississippi is charged with sediment of a different color from that of the Arkansas and Red Rivers, which are tinged with red mud, derived from rocks of porphyry in the far west. The waters of the Uruguay, says Darwin, draining a granitic country are clear and black as those of the Piranha Red. The mud with which the Indus is loaded, says Burns, is of a clay you, that of the Chinab on the other hand is reddish, that of the Sutledge is more pale. The same causes which make these several rivers, sometimes situated at no great distance to one from the other, to differ greatly in the character of their sediment, will make the waters draining the same country at different epics, especially before and after great revolutions in physical geography, to be entirely dissimilar. It is scarcely necessary to add that marine currents will be affected in an analogous manner, in consequence of the formation of new shoals, the emergence of new islands, the subsidence of others, the gradual waste of neighboring coasts, the growth of new deltas, the increase of coral reefs and other changes. Why successive sedimentary groups contain distinct fossils? If in the next place we assume, for reasons before stated, a continual extinction of species and introduction of others into the globe, it will then follow that the fossils of strata formed at two distant periods on the same spot will differ even more certainly than the mineral composition of the same. For rocks of the same kind have sometimes been reproduced in the same district after a long interval of time, whereas there are no facts leading to the opinion that species which have once died out have ever been reproduced. The submergence then of land must be often attended by the commencement of a new class of sedimentary deposits, characterized by a new set of fossil animals and plants. While the reconversion of the bed of the sea into land may arrest at once and for an indefinite time the formation of geological monuments. Should the land again sink, strata will again be formed, but one or many entire revolutions in animal or vegetable life may have been completed in the interval. Conditions requisite for the original completeness of a fossiliferous series. If we infer, for reasons before explained, that fluctuations in the animate world are brought about by the slow and successive removal and creation of species, we shall be convinced that a rare combination of circumstances alone can give rise to such a series of strata as will bear testimony to a gradual passage from one state of organic life to another. To produce such strata, nothing less will be requisite than the fortunate coincidence of the following conditions. First, a never-failing supply of sediment in the same region throughout a period of vast duration. Secondly, the fitness of the deposit in every part for the permanent preservation of embedded fossils. And thirdly, a gradual subsidence to prevent the sea or lake from being filled up and converted into land. It will appear in the chapter on coral reefs that in certain parts of the Pacific and Indian Oceans, most of these conditions, if not all, are complied with and the constant growth of coral keeping pace with the sinking of the bottom of the sea seems to have gone on so slowly for such indefinite periods that the signs of a gradual change in organic life might probably be detected in that quarter of the globe if we could explore its submarine geology. Instead of the growth of coraline limestone, let us suppose in some other place the continuous deposition of fluviatile mud and sand, such as the Ganges and Brahmaputra, have poured for thousands of years into the Bay of Bengal. Part of this bay, although of considerable depth, might at length be filled up before an appreciable amount of change was effected in the fish, mollusca, and other inhabitants of the sea and neighboring land. But if the bottom be lowered by sinking at the same rate that it is raised by fluviatile mud, the Bay can never be turned into dry land. In that case, one new layer of matter may be superimposed upon another for a thickness of many thousand feet, and the fossils of the inferior beds may differ greatly from those entuned in the uppermost, yet every intermediate gradation may be indicated in the passage from an older to a newer assemblage of species. Granting, however, that such an unbroken sequence of monuments may thus be elaborated in certain parts of the sea, and that the strata happen to be all of them well adapted to preserve the included fossils from decomposition, how many accidents must still concur before these submarine formations will be laid open to our investigation? The whole deposit must first be raised several thousand feet in order to bring into view the very foundation, and during the process of exposure the superior beds must not be entirely swept away by denudation. In the first place the chances are as three to one against the mere emergence of the mass above the waters, because three fourths of the globe are covered by the ocean, but if it be upheaved and made to constitute part of the dry land, it must also before it can be available for our instruction become part of that area already surveyed by geologists, and this area comprehends perhaps less than a tenth of the whole world. In this small fraction of land already explored, and still very imperfectly known, we are required to find a set of strata originally of limited extent and probably much lessened by subsequent denudation. Yet it is precisely because we do not encounter at every step the evidence of such gradations from one state of the organic world to another that so many geologists embrace the doctrine of great and sudden revolutions in the history of the animate world. Not content with simply availing themselves for the convenience of classification of those gaps and chasms, which here and there interrupt the continuity of the chronological series. As at present known, they deduce from the frequency of these breaks in the chain of records an irregular mode of succession in the events themselves, both in the organic and inorganic world. But besides that some lengths of the chain which once existed are now clearly lost and others concealed from view, we have good reason to suspect that it was never complete originally. It may undoubtedly be said that strata have been always forming somewhere, and therefore at every moment of past time nature has added a page to her archives. But in reference to the subject it should be remembered that we can never hope to compile a consecutive history by gathering together monuments which were originally detached and scattered over the globe. For as the species of organic beings contemporaneously inhabiting remote regions are distinct, the fossils of the first of several periods may have preserved in any one country, as in America for example will have no connection with those of a second period found in India, and will therefore no more enable us to trace the signs of a gradual change in the living creation than a fragment of Chinese history will fill up a blank in the political annals of Europe. The absence of any deposits of importance, containing recent shells in Chile anywhere in the western coast of South America naturally led Mr. Darwin to the conclusion that where the bed of the sea is either stationary or rising, circumstances are far less favorable than where the level is sinking through the accumulation of conchiferous strata of sufficient thickness and extension to resist the average vast amount of denudation. An examination of the superficial clay, sand and gravel of the most modern date in Norway and Sweden, where the land is also rising, would incline us to admit a similar proposition. Yet in these cases there has been a supply of sediment from the waist of the coast in the interior, especially in Patagonia and Chile. Nevertheless, wherever the bottom of the sea has been continually elevated, the total thickness of sedimentary matter accumulating at depths suited to the habitation of most of the species of shells can never be great, nor can the deposits be thickly covered by super-incumbent matter so as to be consolidated by pressure. When they are upheaved, therefore, the waves on the beach will bear down and disperse the loose materials. Whereas if the bed of the sea subsides slowly, the mass of strata containing abundance of such species as live at moderate depths may increase in thickness to any amount and may extend over a broad area as the water gradually encroaches on the land. If then, at particular periods, as in the Myocene epic, for example, both in Europe and North America, contemporaneous shelly deposits have originated and have been preserved at very distant points. It may arise from the prevalence at that period of simultaneous subsidence throughout very wide areas. The absence in the same quarters of the globe of strata marking the ages which immediately succeeded may be accounted for by supposing that the level of the bed of the sea and the adjoining land was stationary going slow upheaval. How far some of the great violations of continuity which now exist in the chronological table of fossiliferous rocks will hereafter be removed or lessened must at present be mere matter of conjecture. The hiatus, which exists in Great Britain between the fossils of the Lyus and those of the Magnesian limestone, is supplied in Germany by the rich fauna and flora of the Muschelkalk Koepa and Bunter Sandstein, which we know to be of a date precisely intermediate, those three formations being interposed in Germany between others, which agree perfectly in their organic remains with our Lyus and Magnesian limestone. Until lately, the fossils of the coal measures were separated from those of the antecedent Solerian group by a very abrupt and decided line of demarcation, but recent discoveries have brought to light in Devonshire, Belgium, the Eiffel and Westphalia, the remains of a fauna of an intervening period. This connecting link is furnished by the fossil shells, fish and corals of the Devonian or Old Red Sandstone group, and some species of this newly intercalcated fauna are found to be common to it and the subjacent Solerian rocks, while other species belong to it in common with the coal measures. We also have, in like manner, had some success of late years in diminishing the hiatus which still separates the Cretaceous scene periods in Europe. Still, we must expect, for reasons before stated, that some such chasms will forever continue to recur in some parts of our sedimentary series. End of Section 27 Chapter 13 Part 3 of Principles of Geology This is a LibriVox recording. All LibriVox recordings are in the public domain. In order to volunteer, please visit LibriVox.org Principles of Geology by Charles Lyle Chapter 13 Part 3 Consistency of the Theory of Gradual Change with the Existence of Great Breaks in the Series To return to the general argument pursued in this chapter it is assumed for reasons above explained that a slow change of species is in simultaneous operation everywhere throughout the habitable surface of sea and land. Whereas the fossilization of plants and animals is confined to those areas where new strata are produced. These areas, as we have seen, are always shifting their position in the fossilizing process by means of which the commemoration of the particular state of the organic world at any given time is affected may be said to move about visiting and revisiting different tracts in succession. To make still more clear the supposed working of this machinery, I shall compare it to what was imagined to occur in the history of human affairs. Let the mortality of the population of a large country represent the successive extinction of species and the births of new individuals the introduction of new species. While these fluctuations are gradually taking place everywhere, suppose commissioners are appointed to visit each province of the country in succession taking an exact account of the number, names and individual peculiarities of all the inhabitants and leaving in each district a register containing a record of this information. If after the completion of one census another is immediately made on the same plan and then another there will at last be a series of statistical documents in each province. When those belonging to any one province are arranged in chronological order contents of such as stand next to each other will differ according to the length of the intervals of time between the taking of each census. If for example there are 60 provinces and all the registers are made in a single year and renewed annually the number of births and deaths will be so small in proportion to the whole of the inhabitants during the interval between the compiling of the two consecutive documents that the individuals described in such documents will be nearly identical. Whereas if the survey of each of the 60 provinces occupies all the commissioners for a whole year so that they are unable to revisit the same place until the expiration of 60 years there will then be an almost entire discordance between the persons enumerated in two consecutive registers in the same province. There are undoubtedly other causes besides the mere quantity of time which may augment or diminish the amount of discrepancy. Thus at some periods a pestilential disease may have lessened the average duration of human life or a variety of circumstances may have caused the births to be unusually numerous and the population to multiply or a province may be suddenly colonized by persons migrating from surrounding districts. These exceptions may be compared to the accelerated rate of fluctuation in the fauna and flora of a particular region in which the climate and physical geography may be undergoing an extraordinary degree of alteration. But I must remind the reader that the case above proposed has no pretensions to be regarded as an exact parallel to the geological phenomena which I desire to illustrate, for the commissioners are supposed to visit the different provinces in rotation. Whereas the commemorating process by which organic remains become fossilized although they are always shifting from one area to the other are yet very irregular in their movements. They may abandon and revisit many spaces again and again before they once approach another district. And besides this source of irregularity it may often happen that while the depositing process is suspended denudation may take place which may be compared to the occasional destruction by fire or other causes of some of the statistical documents before mentioned. It is evident that where such accidents occur the want of continuity in the series may become indefinitely great and that the monuments which follow next in succession will by no means be equidistant from each other in point of time. If this train of reasoning be admitted the occasional distinctness of the fossil remains in formations immediately in contact would be a necessary consequence of the existing laws of sedimentary deposition and subterranean movement accompanied by a constant mortality and renovation of species. As all the conclusions above insisted on are directly opposed to opinions still popular I shall add another comparison in the hope of preventing any possible misapprehension of the argument. Suppose we had discovered two buried cities at the foot of Vesuvius immediately superimposed upon each other with a great mass of tough and lava intervening just as Portis and Rosina if now covered with ashes would overlie Herculaneum. An antiquary might possibly be entitled to infer from the inscriptions on public edifices that the inhabitants of the inferior and older city were Greeks and those of the modern towns Italians. But he would reason very hastily if he also concluded from these data that there had been a sudden change from the Greek to the Italian language in Campania. But if he afterwards found three buried cities one after the other the intermediate one being Roman while as in the former example the lowest was Greek in the uppermost Italian he would then perceive the fallacy of his former opinion and would begin to suspect that the catastrophes by which the cities were inhumed might have no relation whatever situations in the language of the inhabitants and that as the Roman tongue had evidently intervened between the Greek and Italian so many other dialects may have been spoken in succession and the passage from the Greek to the Italian may have been very gradual. Some terms growing obsolete while others were introduced from time to time. If this antiquary could have shown that the volcanic paroxysms of Vesuvius were so governed as that cities should be buried one above the other just as often as any variation occurred in the language of the inhabitants then indeed the abrupt passage from a Greek to a Roman and from a Roman to an Italian city would afford proof of fluctuations no less sudden in the language of the people. So in geology if we could assume that it is part of the plan of nature to preserve in every region of the globe an unbroken series of monuments to commemorate the vicissitudes of the organic creation we might infer the sudden extirpation of species and the simultaneous introduction of others as often as two formations in contact are found to include dissimilar organic fossils but we must shut our eyes to the whole economy of the existing causes aqueous, igneous and organic if we fail to perceive that such is not the plan of nature. Concluding remarks on the identity of the ancient and present system of terrestrial changes I shall now conclude the discussion of a question with which we have been occupied since the beginning of the fifth chapter namely whether there has been any interruption from the remotest periods of one uniform system of change in the animate and inanimate world. We were induced to enter into that inquiry by reflecting how much the progress of opinion in geology had been influenced by the assumption that the analogy was slight in kind and still more slight in degree between the causes which produced the former revolutions of the globe and those now in everyday operation. It appeared clear that the earlier geologists had not only scanty acquaintance with existing changes but were singularly unconscious of the amount of their ignorance and naturally inspired by this unconsciousness they had no hesitation in deciding at once that time could never enable the existing powers of nature to work out changes of great magnitude still less such important revolutions as those which are brought to light by geology. They therefore felt themselves at liberty to indulge their imaginations in guessing at what might be rather than inquiring what is. In other words, they employed themselves in conjecturing what might have been the course of nature at a remote period rather than investigating of what was the course of nature in their own times. It appeared to them more philosophical to speculate on the possibilities of the past than patiently to explore the realities of the present. And having invented theories under the influence of such maxims they were consistently unwilling to test their validity by the criterion of their accordance with the ordinary operations of nature. On the contrary, the claims of each new hypothesis to credibility appeared enhanced by the great contrast in kind or intensity of the causes referred to and those now in operation. Never was there a dogma more calculated to foster indolence and to blunt the keen edge of curiosity than this assumption of the discordance between the ancient and existing causes of change. It produced a state of mind unfavorable in the highest degree to the candid reception of the evidence minute but incessant alterations which every part of the Earth's surface is undergoing and by which the condition of its living inhabitants is continually made to vary. The student instead of being encouraged with the hope of interpreting the enigmas presented to him in the Earth's structure instead of being prompted to undertake laborious inquiries into the natural history of the organic world and the complicated effects of the igneous and aqueous causes now in operation was taught to despond from the first. Geology it was affirmed could never rise to the rank of an exact science. The greater number of phenomena must forever remain inexplicable or only be partially elucidated by ingenious conjectures. Even the mystery which invested the subject was said to constitute one of its principal charms affording as it did full scope to the fancy to indulge in a boundless field of speculation. The course directly opposed to this method of philosophizing consists in an earnest and patient inquiry. How far geological appearances are reconcilable with the effect of changes now in progress or which may be in progress in regions inaccessible to us and of which the reality is attested by volcanoes and subterranean movements. It also endeavors to estimate the aggregate result of ordinary operations multiplied by time and cherishes a sanguine hope that the resources to be derived from observation and experiment are such as she now is are very far from being exhausted. For this reason all theories are rejected which involve the assumption of sudden and violent catastrophes and revolutions of the whole earth and its inhabitants theories which are restrained by no reference to existing analogies and in which a desire is manifested to cut and then patiently to untie the Gordian knot. We have now at least the advantage of knowing from experience that an opposite method had always put geologists on the road that leads to truth, suggesting views which although imperfect at first have been found capable of improvement until at last adopted by universal consent while the method of speculating state of things and causes has led invariably to a multitude of contradictory systems which have been overthrown one after the other have been found incapable of modification in which have often required to be precisely reversed. The remainder of this work will be devoted to an investigation of the changes now going on in the crust of the earth and its inhabitants. The importance which the student will attach to such researches will mainly depend in the degree of confidence which he feels in the principles above expounded. If he firmly believes in the resemblance or identity of the ancient and present system of terrestrial changes he will regard every fact collected respecting the cause in diurnal action as affording him a key to the interpretation of some mystery in the past. Events which have occurred at the most distant periods in the animate and inanimate world will be acknowledged to throw light on each other and the deficiency of our information respecting some of the most obscure parts of the present creation will be removed. For as by studying the external configuration of the existing land and its inhabitants we may restore in imagination the appearance of the ancient continents which have passed away so we may obtain from the deposits of ancient seas and lakes an insight into the nature of the sub aqueous processes now in operation and of many forms of organic life which though now existing are veiled from sight. Rocks are produced by subterranean fire in former ages at great depths in the bowels of the earth. Present us when upraised by gradual movements and exposed to the light of heaven with an image of those changes which the deep-seated volcano may now occasion in the nether regions. Thus also we are mere sojourners on the surface of the planet chained to a mere point in space enduring but for a moment of time the human mind is not only enabled to number worlds beyond the unassisted can of mortal eye but to trace the events of indefinite ages before the creation of our race and is not even withheld from penetrating into the dark secrets of the ocean or the interior of the solid globe free like the spirit which the poet described as animating the universe. Chapter 14 Part 1 of Principles of Geology 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 Chapter 14 Book 2 Changes in the Inorganic World Aqueous Causes Chapter 14 Division of the subject into changes of the organic and inorganic world Inorganic causes of change divided into aqueous and igneous aqueous causes first consider fall of rain, recent rain prints in mud destroying and transporting power of running water newly formed valleys in Georgia sinuosities of rivers two streams when united do not occupy a bed of double surface in Scotland, floods caused by landslips in the white mountains bursting of a lake in Switzerland devastations caused by the Aeneo at Tivoli excavations in the lavas of Etna by Sicilian rivers gorge of the Cimetto gradual rescission of the cataract of Niagara Division of the subject Geology was defined to be the science which investigates the former changes that have taken place in the organic as well as in the inorganic kingdoms of nature as vicissitudes in the inorganic world are most apparent and as on them all fluctuations in the animate creation must in a great measure depend they may claim our first consideration the great agents of change in the inorganic world may be divided into two principal classes the aqueous and the igneous to the aqueous belong rain rivers, torrents, springs currents and tides to the igneous, volcanoes and earthquakes both these classes are instruments of decay as well as of reproduction but they may also be regarded as antagonist forces for the aqueous agents are incessantly laboring to reduce the inequalities of the earth's surface to a level while the igneous are equally active in restoring the unevenness of the external crust partly by heaping up new matter in certain localities partly by depressing one portion and forcing out another of the earth's envelope it is difficult in a scientific arrangement to give an accurate view of the combined effects of so many forces in simultaneous operation because when we consider them separately we cannot easily estimate either the extent of their efficacy or the kind of results which they produce we are endangered therefore when we attempt to examine the influence exerted singly by each of overlooking the modifications which they produce on one another and these are so complicated that sometimes the igneous and aqueous forces cooperate to produce a joint effect to which neither of them unaided by the other could give rise as when repeated earthquakes unite the earth from running water to widen a valley or when a thermal spring rises up from a great depth and conveys the mineral ingredients with which it is impregnated from the interior of the earth to the surface sometimes the organic combine with the inorganic causes as when a reef composed of shells and corals protects one line of coast from the destroying power of tides or currents and turns them against some other point or when drift timber floated into a lake fills a hollow to which the stream would not have had sufficient velocity to convey earthy sediment it is necessary however to divide our observations on these various causes and to classify them systematically endeavoring as much as possible to keep in view the effects in nature are mixed and not simple as they may appear in an artificial arrangement in treating in the first place of the aqueous causes we may consider them under two divisions first those which are connected with the circulation of water from the land to the sea under which are included all the phenomena of rain, rivers, glaciers, and springs secondly those which arise from the movements of water in lakes, seas, and the ocean wherein are comprised the phenomena of waves, tides, and currents in turning our attention to the former division we find that the effects of rivers may be subdivided into first those of a destroying and transporting and secondly those of a renovating nature in the former are included the erosion of rocks and the transportation of matter to lower levels in the renovating class the formation of deltas by the influx of sediment and the shallowing of seas but these processes are so intimately related to each other that it will not always be possible to consider them under their separate heads fall of rain it is well known that the capacity of the atmosphere to absorb aqueous vapor and hold it in suspension increases with every increment of temperature this capacity is also found to augment in a higher ratio than the augmentation of the heat hence as was first suggested by the geologist Dr. Hutton when two volumes of air both saturated with moisture mingle together clouds and rain are produced for a mean degree of heat having resulted from the union of the two moist airs the excess of vapor previously held in suspension by the warmer of the two is given out and if it be in sufficient abundance is precipitated in the form of rain as the temperature of the atmosphere diminishes gradually from the equator towards the pole the evaporation of water and the quantity of rain diminishes also according to Humboldt's computation the average annual depth of rain at the equator is 96 inches while at latitude 45 degrees it is only 29 inches but there are so many disturbing causes that the actual discharge in any given locality may deviate very widely from this rule in England for example where the average fall at London is 24 and a half inches as ascertained at the Greenwich Observatory there is such irregularity in some districts that while at Whitehaven in Cumberland there fell in 1849 32 inches the quantity of rain in Borodale near Caswick only 15 miles to the westward was no less than 142 inches in like manner in India Colonel Sykes found by observations made in 1847 and 1848 that it places situated between 30 degrees and 18 degrees northern latitude on a line drawn across the western gout in the Deccan the fall of rain varied from 21 to 219 inches the annual average in Bengal is probably below 80 inches yet Dr. G. Hooker witnessed at Turapunji in the year 1850 a fall of 30 inches 24 hours and in the same place during residence of 6 months from June to November 530 inches this occurred in the south face of the Cassia or Garo Mountains in eastern Bengal Seamap chapter 18 where the depth during the whole of the same year probably exceeded 600 inches so extraordinary a discharge of water which as we shall presently see is very local maybe thus accounted for warm southerly winds blowing over the bay of Bengal and becoming laden with vapor during their passage reach the low level delta of the Ganges and Brahmaputra where the ordinary heat exceeds that of the sea and where evaporation is constantly going on from countless marshes and the arms of the great rivers a mingling of two masses of damp air of different temperatures probably causes the fall of 70 or 80 inches of rain which takes place on the plains the monsoon having crossed the delta impinges on the Cassia Mountains which rise abruptly from the plain 4000 and 5000 feet here the wind not only encounters the cold air of the mountains but what is far more effective as a refrigerating cause the aerial current is made to flow upwards and to ascend to a height of several thousand feet above the sea both the air and the vapor contained in it being thus relieved of much atmospheric pressure expands suddenly and are cooled by rarefaction the vapor is condensed and about 500 inches of rain are thrown down annually nearly 20 times as much as falls in Great Britain in a year and almost all of it poured down in six months the channel of every torrent and river is swollen at this season and much sandstone horizontally stratified and other rocks are reduced to sand so great is the superficial waste or denudation that what would otherwise be a rich and luxuriously wooded region is converted into a wild and barren moorland after the current of warm air has been thus drained of a large portion of its moisture it still continues its northerly course to the opposite flank of the Cassia range only 20 miles farther north and here the fall of rain is reduced to 70 inches in the year the same wind then blows northwards across the valley of the Brahmaputra and at length arrives so dry and exhausted at the Bhutan Himalaya latitude 28 degrees north that those mountains up to the height of 5000 feet are naked and sterile and all their outer valleys arid and dusty the aerial current still continuing its northerly course and ascending to a higher region becomes further cooled condensation again ensues and Bhutan above 5000 feet is densely clothed with vegetation in another part of India immediately to the westward similar phenomena are repeated the same warm and humid winds copiously charged with aqueous vapor from the bay of Bengal hold their course due north for 300 miles across the flat and hot plains of the Ganges till they encounter the lofty Sikkim Mountains see map chapter 18 on the southern flank of these they discharge such a deluge of rain and rise 12 feet in as many hours numerous landslips some of them extending 3000 feet across the face of the mountains composed of granite, guineas, and slate descend into the beds of streams and dam them up for a time causing temporary lakes which soon burst their barriers day and night says Dr. Hooker we hear the crashing of falling trees and the sound of boulders thrown violently against each other in the beds of torrents by such wear and tear rocky fragments swept down from the hills are in part converted into sand and fine mud and the turban Ganges during its annual inundation derives more of its sediment from this source than from the waste of the fine clay of the alluvial plains below on the verge of the tropics a greater quantity of rain falls annually than at the equator when yet parts even of the tropical latitudes are entirely destitute of rain Peru for example which owes its vegetation solely to rivers and nightly dews in that country easterly winds prevail blowing from the Pacific and these being intercepted by the Andes and cooled as they rise are made to part with all their moisture before reaching the low region to the leeward the desert zone of North Africa between latitude 15 degrees and 30 degrees north is another instance of a rainless region 5 or 6 consecutive years may pass in Upper Egypt, Nubia or Dungola or in the desert of Sahara without rain from the facts above mentioned the reader will infer that in the course of successive geological periods there will be great variations in the quantity of rain falling in one and the same region at one time there may be none of whatever during the whole year at another of all of 100 or 500 inches and these two last averages may occur on the two opposite flanks of a mountain chain not more than 20 miles wide while therefore the valleys in one district are widened and deepened annually they may remain stationary in another the superficial soil being protected from waste by a dense covering of vegetation this diversity depends on many geographical circumstances but principally on the height of the land above the sea the direction of the prevailing winds and the relative position at the time being of the plains, hills and the ocean conditions all of which are liable in the course of ages to undergo a complete revolution recent rain prints when examining in 1842 the extensive mud flats of Nova Scotia which are exposed at low tide on the borders of the Bay of Fundy I observed not only the footprints of birds which had recently passed over the mud but also very distinct impressions of raindrops a peculiar combination of circumstances renders these mud flats admirably fitted to receive and retain any markings which may happen to be made on their surface the sediment with which the waters are charged is extremely fine being derived from the destruction of cliffs of red sandstone and shale and as the tides rise 50 feet and upwards large areas are laid dry for nearly a fortnight between the spring and neap tides in this interval the mud is baked in summer by a hot sun so that it solidifies and becomes traversed by cracks caused by shrinkage portion of the hardened mud between these cracks may then be taken up and removed without injury on examining the edges of each slab we observe numerous layers formed by successive tides each layer being unusually very thin sometimes only one tenth of an inch thick when a shower of rain falls the highest portion of the mud covered flat is usually too hard to receive any impressions while that recently uncovered by the tide near the water's edge is too soft between these areas a zone occurs almost as smooth and even as a looking glass on which every drop forms a cavity of circular or oval form and if the shower be transient these pits retain their shape permanently being dried by the sun and being then too firm to be effaced by the action of the succeeding tide which deposits upon them a new layer of mud hence we often find in splitting open a slab an inch or more thick on the upper surface which the marks of recent rain occur that an inferior layer deposited during some previous ride of the tide exhibits on its underside perfect casts of rain prints which stand out in relief the molds of the same being seen on the layer below but in some cases especially in the more sandy layers the markings have been somewhat blunted by the tide and by several rain prints having been joined into one by a repetition of drops falling on the same spot in which case the casts present a very irregular and blistered appearance the finest examples which I have seen of these rain prints were sent to me by Dr. Webster from Kentville on the borders of the Bay of Mines in Nova Scotia they were made by a heavy shower which fell on the 21st of July, 1849 when the rise and fall of the tides were at their maximum the impressions, see figure 13 consist of cup shaped or hemispherical cavities the average size of which is from 1 eighth to 1 tenth of an inch across but the largest are fully half an inch in diameter and 1 tenth of an inch deep the depth is chiefly below the general surface or plane of stratification but the walls of the cavity consist partly of a prominent rim of sandy mud formed of the matter which has been forcibly expelled from the pit all the cavities having an oval form are deeper at one end where they have also a higher rim and all the deep ends have the same direction showing towards which quarter the wind was blowing two or more drops are sometimes seen to have interfered with each other in which case it is usually possible to determine which drop fell last its rim being unbroken on some of the specimens the winding tubular tracks of worms are seen which have been bored just beneath the surface see figure 13, left side they occasionally pass under the middle of a rain mark having been formed subsequently sometimes the worms have dived beneath the surface and then reappeared all these appearances both of rain prints and worm tracks are of great geological interest as their exact counterparts are seen in rocks of various ages even in formations of very high antiquity small cavities often corresponding in size to those produced by rain are also caused by air bubbles rising up through sand or mud but these differ in character from rain prints being usually deeper than they are wide and having their sides steeper these indeed are occasionally vertical or overarching the opening at the top being narrower than the pit below in their mode also of mutual interference they are unlike rain prints in consequence of the effects of mountains in cooling currents of moist air and causing the condensation of aqueous vapor in the manner above described it follows that in every country as a general rule the more elevated regions become perpetual reservoirs of water which descends and irrigates the lower valleys and plains the largest quantity of water is first carried to the highest region and then made to descend by steep declivities towards the sea so that it acquires superior velocity and removes more soil than it would do if the rain had been distributed over the plains and mountains equally in proportion to their relative areas the water is also made by these means to pass over the greatest distances before it can regain the sea it has already been observed that in higher latitudes where the atmosphere being colder is capable of holding less water in suspension a diminished fall of rain takes place thus at St. Petersburg the amount is only 16 inches and at Uliaborg in the Gulf of Botnia northern latitude 65 degrees only 13 and a half inches or less than half the average of England and even this small quantity descends more slowly in the temperate zone and is spread more equally over the year than in tropical climates but in reference to geological changes frost in the colder latitude acts as a compensating power in the disintegration of rocks and the transportation of stones to lower levels water when converted into ice augments in bulk more than one twentieth of its volume and owing to this property it widens the minute crevices or joints of rocks into which it penetrates ice also in various ways as will be shown in the next chapter gives buoyancy to mud and sand even to huge blocks of stone enabling rivers of moderate size and velocity to carry them a great distance the mechanical force exerted by running water into undermining cliffs and rounding off the angles of hard rock is mainly due to the intermixture of foreign ingredients sand and pebbles when hurried along by the violence of the stream are thrown against every obstacle lying in their way and thus a power of attrition is acquired capable of wearing through the hardest Silicius stones on which water alone could make no impression End of chapter 14 part 1