proved by contemporary monuments—as in history—summary of historical evidence—geological evidence of human periods—neolithic period—pal?olithic or quaternary—tertiary—secondary and older periods—the recent or post-glacial period—lake-villages—bronze age—kitchen-middens—scandinavian peat-mosses—neolithic remains comparatively modern—definition of post-glacial period—its duration—mellard read's estimate—submerged forests—changes in physical geography—huxley—objections from america—niagara—quaternary period—immense antiquity—presence of man throughout—first glacial period—scandinavian and laurentian ice-caps—immense extent—mass of débris—elevation and depression—in britain—inter-glacial and second glacial periods—antiquity measured by changes of land—lyell's estimate—glacial débris and loess—recent erosion—bournemouth—evans—prestwich—wealden ridge and southern drift—contain human implements—evidence from new world—california.
we have now to take leave of historical records and fall back on the exact sciences for further traces of human origins. our guides are still contemporary records, but these are no longer stately tombs and temples, massive pyramids and written inscriptions. instead of these we have flint implements, incised bones, and a few rare specimens of human skulls and skeletons, the meaning of which has to be deciphered 261 by skilled experts in their respective departments of science.
still these records tell their tale as conclusively as any hieroglyphic or cuneiform writings in egyptian manuscripts or on babylonian cylinders. the celt, the knife, the lance and arrow-heads, and other weapons and implements, can be traced in an uninterrupted progressive series from the oldest and rudest pal?olithic specimens, up to the highly-finished ones of polished stone, and through these into the age of metals, and into historic times and the actual implements of existing savage races. it is impossible to doubt that one of the pal?olithic celts from st. acheul or st. prest is as truly a work of the human hand, guided by human intelligence, as a modern axe; and that an arrow-head from moustier or kent's cavern is no more an elf-bolt, or a lusus natur?, than is a winchester rifle.
before entering on this new line of investigation, it may be well to sum up briefly the evidence as to the starting-point from history and tradition. the commencement of the strictly historical period takes us back certainly for 6000 and in all probability for 7000 years in egypt, and certainly for 5000 and probably for 6000 or 7000 years in chald?a. in each case we find populous cities, important temples and public works, writing and other advanced arts and industries, and all the signs of an old civilization already existing. other nations also evidently then existed with whom these ancient empires had relations of war and of commerce, though the annals of even the oldest of them, such as china, do not carry us back further than from 4000 to 5000 years.
traditions do not add much to our information from monuments, and fade rapidly away into myths and 262 legends. the oldest and most authentic, those of egypt, simply confirm the inference of great antiquity for its civilization prior to menes, but give no clue as to its origin. they neither trace it up to the stone age, which we know existed in the valley of the nile, nor refer it to any foreign source. the egyptian people thought themselves autochthonous, and attributed their arts, industries, and sciences to the inventions of native gods, or demi-gods, who reigned like mortal kings, in a remote and fabulous antiquity. we can gather nothing therefore from tradition that would enable us to add even 1000 years with certainty to the date of menes; while from the high state of civilization which had been evolved prior to his accession, from the primitive conditions of the stone period whose remains are found at cairo and thebes, we might fairly add 10,000 or 20,000 years to his date of 5004 years b.c., as a matter of probable conjecture for the first dawn of historical civilization. in any case we shall be well within the mark if we take 10,000 years as our first unit, or standard of chronological measurement, with which to start in our further researches, as we do with terrestrial standards in gauging the distances of suns and stars.
it may be well also to supplement this statement of the historical standard by a brief review of the previous geological periods through which evidences of man's existence can be traced. immediately behind the historic age lies the recent period during which the existing fauna and flora, climate and configuration of seas and lands, have undergone no material change. it is characterized generally as the neolithic period, in which we find polished stone superseding the older and ruder forms of chipped stone, and passing itself into the 263 copper, bronze, and iron ages of early history. it may also be called the recent or post-glacial period, for it coincides with the final disappearance of the last great glaciation, and the establishment of conditions of climate resembling those of the present day.
behind this again comes the quaternary or pleistocene period, so called from its fauna, which, although containing extinct species, shows along with them many existing forms, some of which have migrated and some remain. this also may be called the glacial period, for although the commencement, termination, and different phases of the two great glaciations and intermediate inter-glacial periods cannot be exactly defined, and hard-and-fast lines drawn between the later pliocene at one end and the post-glacial at the other, there is no doubt that in a general way the quaternary and glacial periods coincide, and that the changes of climate were to a considerable extent the cause of the changes of flora and fauna.
behind the quaternary comes in the tertiary, with its three great divisions of pliocene, miocene, and eocene, each containing numerous subdivisions, and all showing a progressive advance in forms of life, from older and more generalized types towards newer and more specialized ones, and a constant approach towards genera and species now existing. behind the tertiary comes the secondary period, into which it is unnecessary to enter for the present purpose, for all is different, and even mammalian life is only known to be present in a few forms of small and feeble marsupials. nor is it necessary to enter on any detailed consideration of the eocene or earlier tertiary, for the types of mammalian life are so different from those of later periods, that it 264 cannot be supposed that any animal so highly organized as man had then come into existence. the utmost we can suppose is that, as in the case of the horse, some ancestral form from which the quadrumana and man may possibly have been developed may be found. but up to the present time nothing has been found in the eocene more nearly approaching such a missing link than an ancient form of lemur; and it is not until we get into the miocene that any evidence presents itself that man, or some near ancestor of man, may possibly have existed.[8]
my present object being not to write a book on geology, but on human origins, i shall not attempt to trace back the geological evidence beyond the miocene, or to enter on any details of the later periods, except so far as they bear on what may be called geological chronology, i.e. on the probable dates which may be assigned to the first appearance and subsequent evolution of the human race going back from historical times.
beginning with the recent or post-glacial period, 265 the swiss and italian lake-villages supply clear evidence of the progress of man in western europe through the neolithic into the historical period. they afford us an unbroken series of substantially the same state of society, existing down to the time of the romans, for a great many centuries back of communities living in lake-villages built upon piles, like the villages in thrace described by herodotus, or those of the present day in new guinea. some of these have been occupied continuously, so that the débris of different ages are stored in consecutive order like geological strata, and afford an unerring test of their relative antiquity. it is clear that many of those lake-villages were founded in the age of stone, and passed through that of bronze into the age of iron. the oldest settlements belong to the neolithic age, and contain polished stone implements and pottery, but they show a state of civilization not yet very far advanced. the inhabitants were only just emerging from the hunting into the pastoral stage. they lived principally on the produce of the chase, the bones of the stag and wild boar being very plentiful, while those of ox and sheep are rare. agriculture and the cereals seem to have been unknown, though stores of acorns and hazel nuts were found which had been roasted for food.
by degrees the bones of wild animals become scarce, and those of ox and sheep common, showing that the pastoral stage had been reached; and the goat, pig, and horse were added to the list of domestic animals—the dog being included from the first, and the horse only at a later period. agriculture follows next in order, and considerable proficiency was attained, barley and wheat being staple articles of food, and apples, pears, and other fruit being stored for winter consumption. flax also 266 was grown, and the arts of spinning and weaving were introduced, so that clothing, instead of being confined to skins, was made of coarse linen and woollen stuffs.
the most important advance, however, in the arts of civilization is afforded by the introduction of metals. these begin to appear about the middle of the neolithic period, at first very sparingly, and in a few districts such as spain, upper italy, and hungary, where native copper was found and was hammered into shapes modelled on the old stone implements; but as a general rule, and in all the later settlements, bronze, in new and improved shapes, supersedes stone and copper. for the most part these bronze implements seem to have been obtained by foreign commerce from the ph?nicians, etruscans, and other nations bordering on the mediterranean, though in some cases they were cast on the spot from native or imported ores. the existence of bronze, however, must go back to a far greater antiquity than the time when the neolithic people of europe obtained their first supplies from ph?nician traders. bronze, as we have seen in a former chapter, is an alloy of two metals, copper and tin, and the hardest and most serviceable alloy is only to be obtained by mixing the two in a certain definite proportion. now it is to be noted, that nearly all the prehistoric bronze found in europe is an alloy in this definite proportion. clearly all this bronze, or the art of making it, must have originated from some common centre.
all this, however, is very conjectural, and all that can be concluded from it is, that any indications as to the antiquity of man derived from the bronze age as known to us in europe, hardly carry us back to dates as remote as those furnished by the monuments of egypt 267 and chald?a. indeed, there are no facts certainly known to us from remains of the bronze age in europe that imply a greater antiquity than 1500 or possibly 2000 years b.c., a date at which bronze had undoubtedly been already known in egypt and the east for many centuries.
the neolithic period which preceded that of metals is of longer duration, but still comparatively recent. attempts have been made to measure it by a sort of natural chronometer in the case of the lake-villages, by comparing the amount of silting up since the villages were built with the known rate of silting up since roman times. the calculations vary very much, and can only be taken as approximative; but the oldest dates assigned do not exceed 5000 b.c., and most of them are not more than 2000 or 3000 b.c. it must be remembered however that the foundation of a lake-village on piles implies a long antecedent neolithic period, to have arrived at a stage of civilization which made the construction of such villages possible.
this civilization coincides wonderfully with that of the primitive aryans as shown by linguistic pal?ontology. the discussion as to the origin of the aryans has thrown a great deal of light on this question, and has gone far to dispel the old notion that they radiated from some centre in asia, and overran europe in successive waves. on the contrary, all the evidence and all the best authorities point to their having occupied, when we first get traces of them, pretty much the same districts of the great plain of northern europe and southern russia as we now find them in, and developed there their distinct dialects and nationalities; while the words common to all or nearly all the aryan families point 268 to their having been pastoral nomads, in a state of civilization very like that of the earlier lake-villagers, before this separation took place.
the scandinavian kitchen-middens, or shell-mounds, carry us further back into this early neolithic period. the shell-mounds which are found in great numbers along the baltic shore of denmark are often of great size. they are formed of an accumulation of shells of oysters, mussels, and other shell-fish, bones of wild animals, birds, and fish, all of existing species, with numerous implements of flint or bone, and occasional fragments of coarse pottery. they are decidedly more archaic than the lake-dwellings, showing a much ruder civilization of savages living like the fuegians of the present day, in scanty tribes on the sea-shore, supported mainly by shell-fish, supplemented by the chase of wild animals.
the dog was their only domestic animal, and their only arts the fabrication of rude pottery and implements of stone and bone, unless it can be inferred from the occasional presence of bones of cod and other deep-sea fish, that they possessed some form of boat or canoe, and had hooks and lines or nets. these mounds must have taken an enormous time to accumulate, for they are very numerous, and often of great bulk, some of them being 1000 feet long, 200 feet wide, and ten feet thick. how long such masses must have taken to accumulate must be apparent when we consider that the state of civilization implies a very scanty population. it has been calculated that if the neolithic population of denmark required as many square miles for its support as the similar existing populations of greenland and patagonia, their total number could not have 269 exceeded 1000, and each mound must have been the accumulation of perhaps two or three families. ancient, however, as these mounds must be, they are clearly neolithic. they are sharply distinguished from the far older remains of the pal?olithic period by the knowledge, however rude, of pottery and polished stone, and still more by the fauna, which is entirely recent, and from which the extinct animals of the quaternary period have disappeared; while the position of the mounds shows that only slight geological changes, such as are now going on, have occurred since they were accumulated. similar mounds, on even a larger scale, occur on the sea-coasts of various districts in europe and america, but they afford no indication of their date beyond that of great antiquity.
the peat-mosses of denmark have been appealed to as affording something like a conjectural date for the early neolithic period in that country. these are formed in hollows of the glacial drift, which have been small lakes or ponds in the midst of forests, into which trees have fallen, and which have become gradually converted into peat by the growth of marsh plants. it is clearly established that there have been three successive ages of forest growth, the upper one of beech, below it one of oak, and lowest of all one of fir. the implements and relics found in the beech stratum are all modern, those in the oak stratum are of the later neolithic and bronze ages, and those in the lowest, or fir-horizon, are earlier and ruder neolithic, resembling those found in the older lake-villages and shell-mounds. now beech has been the characteristic forest tree of denmark certainly since the roman period, or for 2000 years, and no one can say for how much longer. if the speculations 270 as to the origin of the aryan race in northern europe are correct, it must have been for very much longer, as the word for beech is common to so many of the dialects into which the primitive aryan language became divided. the stages of oaks and firs must equally have been of long duration, and the different stages could only have been brought about by slow secular variations of climate during the post-glacial period. still this affords no reliable information as to specific dates, and we can only take steenstrup's calculation of from 4000 to 16,000 years for the formation of some of these peat-bogs as a very vague estimate, and this only carries us back to a time when egypt and chald?a must have been already densely peopled, and far advanced in civilization.
on the whole, it seems that the neolithic arrow-heads found in egypt, and the fragments of pottery brought up by borings through the deposits of the nile, are the oldest certain human relics of the neolithic age which have yet been discovered, and these do not carry us back further than a possible date of 15,000 or 20,000 years b.c.
nor is there any certainty that any of the neolithic remains found in the newer deposits of rivers and the upper strata of caves go further, or even so far back as these relics of an egyptian stone period. all that the evidence really shows is, that while the neolithic period must have lasted for a long time as compared with historical standards, its duration is almost infinitesimally small as compared with that of the preceding pal?olithic period. thus in kent's cavern neolithic remains are only found in a small surface layer of black earth from three to twelve inches thick; while below this, pal?olithic 271 implements and a quaternary fauna occur in an upper stalagmite one to three feet thick, below it in red cave earth five to six feet thick; then in a lower stalagmite in places ten or twelve feet thick, and below it again in a breccia three or four feet thick. this is confirmed by the evidence of all the caves explored in all parts of the world, which uniformly show any neolithic remains confined to a superficial layer of a few inches with many feet of pal?olithic strata below them. and river-drifts in the same manner show neolithic remains confined to the alluvia and peat-beds of existing streams, while pal?olithic remains occur during the whole series of deposits while these rivers were excavating their present valleys. if we say feet for inches, or twelve for one, we shall be well within the mark in estimating the comparative duration of the pal?olithic and neolithic periods, as measured by the thickness of their deposits in caves and river-drifts; and as we shall see hereafter, other geological evidence from elevations and depressions, denudations and depositions, point to even a higher figure.
in going back from the neolithic into the pal?olithic period, we are confronted by the difficulty to which i have already referred, of there being no hard-and-fast lines by which geological eras are clearly separated from one another. zoologically there seems to be a very decided break between the recent and the quaternary. the instances are rare and doubtful in which we can see any trace of the remains of pal?olithic man, and of the fauna of extinct animals, passing gradually into those of neolithic and recent times. but geologically there is no such abrupt break. we cannot draw a line at the culmination of the last great glaciation and say, here the glacial period ends and the post-glacial begins. 272 nor can we say of any definite period or horizon, this is glacial and this recent.
a great number of pal?olithic remains and of quaternary fossils are undoubtedly post-glacial in the sense of being found in deposits which have accumulated since the last great glaciers and ice-caps began to retreat. existing valleys have been excavated to a great extent since the present rivers, swollen by the melting snows and torrential rains of this period of the latest glacial retreat, superseded old lines of drainage, and began to wear down the surface of the earth into its present aspect. this phase is more properly included in the term glacial, for both the coming on and the disappearance of the periods of intense cold are as much part of the phenomenon as their maximum culmination, and very probably occupied much longer intervals of time. in like manner, we cannot positively say when this post-glacial period ended and the recent began. not, i should say, until the exceptional effects of the last great glacial period had finally disappeared, and the climate, geographical conditions, and fauna had assumed nearly or entirely the modern conditions in which we find them at the commencement of history. and this may have been different in different countries, for local conditions might make the glacial period commence sooner and continue later in some districts than in others. thus in north america, where the glaciation was more intense, and the ice-cap extended some ten degrees further south than in europe, it might well be that it was later in retreating and disappearing. the elevation of the laurentian highlands into the region of perpetual snow was evidently one main factor of the american ice-cap, just as that of scandinavia was of that of europe, and it by no 273 means follows that their depression was simultaneous. it would be unwise, for instance, to take the time occupied in cutting back the niagara gorge by a river which only began to run at some stage of the post-glacial period, as an absolute test of the duration of that period all over the world. indeed, the glacial period cannot be said to have ended and the post-glacial begun at the present day in greenland, if the disappearance of the ice-cap over very extensive regions is to be taken as the test.
any approximation to the duration of the post-glacial period in any given locality can only be obtained by defining its commencement with the first deposits which lie above the latest glacial drift, and measuring the amount of work done since.
this has been done very carefully by the officers of the geological survey and other eminent authorities in england and scotland, and the result clearly shows that since the last glaciation left the country buried in a thick mantle of boulder-clay and drift, such an amount of denudation, and such movements of elevation and depression have taken place, as must have required a great lapse of time. the most complete attempt at an estimate of this time is that made by mr. mellard read of the geological survey, from the changes proved to have occurred in the mersey valley.
in this case it is shown that the valley, almost in its present dimensions, must have been first carved out of an uniform plain of glacial drift and upper boulder-clay by sub-a?rial denudation; then that a depression let the sea into the valley and accumulated a series of estuarine clays and silts; then an elevation raised the whole into a plain on which grew an extensive forest of 274 oak rooted in the clays; this again must have subsided and let in the sea for a second time, which must have remained long enough to leave a large estuarine deposit, and finally the whole must have been raised to the present level before historical times. the phenomenon of the submerged forest is a very general one, being traced along almost all the sea-coasts of western europe, where shelving shores and sheltered bays favour the preservation of patches of this prim?val forest. it testifies to a considerable amount of elevation and subsequent depression, for its remains can be traced below low-water mark, and are occasionally dredged up far out to sea, and stately oaks could not have flourished unless more or less continental conditions had prevailed.
it is evident that in this age of forests the german ocean must have been dry land, and the continent of europe must have extended beyond the orkneys and hebrides, probably to the hundred fathom line. such movements of elevation and depression, so far as we know anything of them, are extremely slow. there has been no change in the fords of rivers in britain since roman times, and the spit connecting st. michael's mount with cornwall was dry at ebb and covered at flood as at the present day, when the british carted their tin across it to trade with the ph?nicians 2500 years ago. mr. read goes into elaborate calculations based on the time required for these geological changes, and arrives at the conclusion that they point to a date of not less than 50,000 or 60,000 years ago for the commencement of the post-glacial period. these calculations are disputed, but it seems certain that several multiples of the historical standard of say 10,000 years, must be required to measure the period since the 275 glacial age finally disappeared, and the earth, with its existing fauna, climate, and geographical conditions, came fairly into view. this is confirmed by the great changes which have taken place in the distribution of land and water since the quaternary period. huxley, in an article on the aryan question, points out that in recent times four great separate bodies of water—the black sea, the caspian, the sea of aral, and lake balkash—occupied the southern end of the vast plains which extend from the arctic sea to the highlands of the balkan peninsula, of asia minor, of persia and afghanistan, and of the high plateaux of central asia, as far as the altai. but he says, "this state of things is comparatively modern. at no very distant period the land of asia minor was continuous with that of europe, across the present site of the bosphorus, forming a barrier several hundred feet high, which dammed up the waters of the black sea. a vast extent of eastern europe and of west-central asia thus became one vast ponto-aralian mediterranean, into which the largest rivers of europe and asia, the danube, volga, oxus, and jaxartes, discharged their waters, and which sent its overflow northwards through the present basin of the obi." the time necessary for such changes goes far to confirm mellard read's estimate for the long duration of the recent or post-glacial period.
in fact, all the evidence from the old world goes to confirm the long duration of the post-glacial period, and the immensely greater antiquity of the glacial period taken as a whole. it is only from the new world that any serious arguments are forthcoming to abridge those periods, or rather the post-glacial period, for that alone is affected by the facts adduced. it is said that recent 276 measurements of the recession of the falls of niagara show, that instead of requiring 35,000 years, as estimated by lyell, to cut back the gorge of seven miles from kingston to the falls, 10,000 years at the outside would have been amply sufficient; and that this is confirmed by the gorges of other rivers, such as that of the mississippi at st. paul's. the evidence is not conclusive, for it depends on the rate of erosion going on for the last twenty or thirty years, which may obviously give a different result from the true average, and in fact older estimates, based on longer periods, gave the rate adopted by lyell. but if we admit the accuracy of the modern estimates, it does not affect the total duration of the glacial period, but simply that of a late phase of the post-glacial, when the ice-cap which covered north america to a depth often of 2000 or 3000 feet, had melted away and shrunk back 400 miles from its original southern boundary, so as to admit of the waters of the great lakes finding an outlet to the north-east instead of by the old drainage to the south. nothing is more likely than that, as the great laurentian ice-cap of america was deeper and extended further than the scandinavian ice-cap of europe, it may have taken longer to melt the larger accumulation of ice, and thus postponed the establishment of post-glacial conditions and river-drainage to a later period than in the warmer and more insular climate of europe. it is a matter of everyday observation, that the larger a snowball is the longer it takes to melt, and that when the mass is large it requires a long time to make it disappear even after mild weather has set in.
the only other argument for a short glacial period is drawn from the rate of advance of the glaciers in 277 greenland, which is shown to be much more rapid than that of the glaciers of switzerland, from which former calculations had been made. but obviously the rate at which the fronts of glaciers advance when forced by a mass of continental ice down fiords on a steep descending gradient, into a deep sea, where the front is floated off in icebergs, affords no clue as to that of an ice-cap spread, with a front of 1000 miles, over half a continent, retarded by friction, and surmounting mountain chains 3000 feet high. nor does the rate of advance afford the slightest clue to the time during which the ice-cap may have remained stationary, alternately advanced and retreated, and finally disappeared.[9]
278 we have now to adjust our time-telescope to a wider range, and see what the quaternary or glacial period teaches us as to the antiquity of man. the first remark is, that if the post-glacial period is much longer than that for which we have historical records, the glacial exceeds the post-glacial in a far higher proportion. the second, that throughout the whole of this glacial period, from its commencement to its close, we have conclusive evidence of the existence of man, and that not only in a few limited localities, but widely spread over nearly all the habitable regions of the earth.
the first point has been so conclusively established by all geologists of all countries, from the time of lyell down to the present day, that it is unnecessary to enter on any detailed arguments, and the leading facts may be taken as established. it may be sufficient, therefore, if i give a short summary of those facts, and quote a few of the instances which show the enormous lapse of time which must have elapsed between the close of the tertiary and the commencement of the modern epoch.
the glacial period was not one and simple, but comprised several phases. during the pliocene the climate was gradually becoming colder, and either towards its close or at the commencement of the quaternary, this culminated in a first and most intense glaciation. ice-caps radiating from scandinavia crept outwards, filling up the north sea, crossing valleys and mountains, and covering with their boulders and moraines a wide circle, embracing britain down to the thames valley, germany to the hartz mountains, and russia almost as far east as the urals. in north 279 america a still more massive ice-cap overflowed mountain ranges 3000 feet high, and covered the whole eastern half of the continent with an unbroken mantle of ice as far south as new york and washington.
at the same time every great mountain chain and high plateau sent out enormous glaciers, which, in the case of the alps, filled up the valley of the rhone and the lake of geneva, buried the whole of the lower country of switzerland under 3000 feet of ice, and left the boulders of its terminal moraine, carried from the mont blanc range, at that height on the opposite range of the jura. nor is this a solitary instance. we find everywhere traces of enormous glaciers in the pyrenees and carpathians, the atlas and lebanon, the taurus and caucasus, the highlands of scotland, ireland, and wales; in the rocky mountains and sierra nevada; the andes and cordilleras of south america; in south africa and in new zealand. these may not have all been simultaneous, but they certainly all belong to the same period of the great glaciation, and show that it must have been affected by some general cause, and not been entirely due to mere local accidents.
how this first great glacial period came on, or how long it lasted, we do not know, unless croll's astronomical theory, which will be considered later, affords a clue. but we know generally that it must have lasted for an immense time from the amount of work done and the changes which took place. the ice, which covered so great a portion of the northern hemisphere, was not a polar ice-cap, but spread outwards in all directions from great masses of elevated land, as is proved conclusively from the direction of the stri? which were engraved by it on the subjacent rocks. this land must have been 280 more elevated than at present, so as to rise, like greenland, far into the region of perpetual snow, where all rain falls and accumulates in the solid form; and also to supply the enormous mass of débris which the ice-caps and glaciers left behind them. it is not too much to say that a million of square miles in europe, and more in north america, were covered by the débris of rocks ground down by these glaciers, and often to great depths. most of the débris of the first glaciation have been removed by denudation, or ploughed out by the second great advance of the ice, leaving only the larger and harder boulders to testify to their extent; but enough remains to show that the first series of boulder-clays and drifts must have been on a scale larger than those of the second and subsequent glaciations, which now form the superficial stratum of so much of the earth's surface, and often attain a depth of several hundred feet. wright, in his ice age in north america, estimates that "not less than 1,000,000 square miles of territory in north america is still covered with an average depth of fifty feet of glacial débris."
however, this first period of elevation and of intense glaciation passed away, and was succeeded by one of depression and of milder climate. whether or no the depression was due, as some think, to the weight of the enormous mass of ice weighing down the yielding crust of the earth, and whether or no the milder climate was partly occasioned by this depression letting in the sea, the fact is certain that the two coincided, and were general and not merely local phenomena. marine shells at the top of what are now high hills, and which during the preceding glaciation were probably higher, attest the fact that a large amount of land must have sunk 281 below the sea towards the close of this first glacial period. it is equally clear that a long inter-glacial period ensued, during which many changes took place in the geographical conditions and in the fauna and flora, requiring a very long time. thus britain, which had been reduced to an arctic archipelago, in which only a few of the highest mountain peaks emerged as frozen islands, became united to the continent, and the abode of a fauna consisting in great part of african animals. at one time boreal shells were deposited, at the bottom of an arctic ocean, on what is now the top of moel-tryfen in wales, a hill 1300 feet above the present sea-level; while at another the hippopotamus found its way, in some great river flowing from the south, as far north as yorkshire, and the remains of african animals such as the hyena accumulated in our caves. in southern france we had at one time a vegetation of the arctic willow and reindeer moss, at another that of the fig-tree and canary-laurel. when we consider that little if any change has occurred either in geographical conditions or in fauna or flora, within the historical period of some 10,000 years, it is difficult to assign the time which would be sufficient to bring about such changes by any known natural causes. and yet it comprises only a portion of the glacial period, for after this inter-glacial period had lasted for an indefinite time the climate again became cold, and culminated in a second glaciation, which, if not equal to the first, was still of extreme severity, and brought back ice-caps and glaciers almost to their former limits, passing away slowly and with several vicissitudes and alternate retreats and advances.
it is not always easy to determine the position of each individual phase of the two glacial and the inter-glacial 282 periods, for they must often be intermixed, and the results of the last glaciation and of subsequent denudation have to a great extent obscured those of the earlier periods. but taking a general view of the glacial period as a whole, there are a few leading facts which testify conclusively to its immense antiquity. first, there is the amount of elevation and depression. we have seen that marine arctic shells have been found on the top of moel-tryfen, 1300 feet above the present sea-level. nor is this an isolated instance, for marine drifts apparently of the same character have been traced on the mountains of scotland, wales, and ireland to a height of between 2000 and 3000 feet. in norway, also, old sea beaches are found up to a height of 800 feet. nor are these great movements confined to the old world or to limited localities. according to professor le conte, at the last meeting of the geological congress at washington, a great continental movement, commencing in the later tertiary and terminating in the beginning of the quaternary, caused changes of level amounting to 2500 or 3000 feet on both sides of the continent of north america.
now elevation and depression of large masses of land are, as far as we know anything certain about them, very slow processes, especially in countries unaffected by recent volcanic action, which is the case with nearly all the regions in north america and europe which were covered by the great ice-sheets. there has been little or no perceptible change anywhere since the commencement of history, and the only accurate measurements of changes now going on are those made in sweden, where it appears that in some cases elevation, and in others depression, is taking place at the rate of about two and 283 a half feet in a century. in volcanic regions earthquakes have occasionally caused movements of greater amount in limited areas, but there is no trace of anything of the sort in these movements of the glacial period which have apparently gone on by slight secular changes in the earth's crust as they are now doing in scandinavia.
but in this case a depression of 2000 feet, followed by an elevation of equal amount, at lyell's rate of two and a half feet per century, would require 160,000 years, without allowing for any pauses during the process. and this only embraces part of the whole glacial period, for the depression did not begin until after the climax of the first great glaciation, when the land probably stood higher than at present. of course the actual movements may have been more rapid, but unless we resort to the exploded theories of cataclysms and catastrophes, the time for such movements must have been very great.
an equally conclusive proof of the immense antiquity of the glacial period is afforded by the formation known as the loess, which fills up so many of the valley systems of europe, asia, and america to great depths, and spreads over the adjacent table-lands. it is a tranquil land deposit of fine glacial mud, from sheets of water which inundated the country when great rivers from glaciated districts ran at higher levels, and began to excavate their present valleys. lyell estimates the thickness of this deposit in the rhine valley at 800 feet, and it is found at much higher levels on upland plains. now this loess is not a marine or lacustrine deposit, as is proved by the shells it contains, which are all of land species; nor is it a deposit of running water, for there are no sands or gravels, but distinctly such a deposit 284 from tranquil sheets of muddy water as is now accumulated in egypt by the inundations of the nile. when the rhine brought down such volumes of muddy water from the glaciers of the alps as to overflow the upland plains, it must have flowed at a level many hundred feet higher than its present valley, which must have been since scooped out by sub-a?rial denudation. the rate of deposition of the nile mud is about three inches per century, and there seems no reason why that of the fine glacial mud should have been more rapid, charged as the nile is every year with mud from the torrential rains of the abyssinian highlands. at this rate it would have required 320,000 years to accumulate the 800 feet of loess of the rhine valley. here again the rate may have been faster, but it is sufficient to show that an immense time must have elapsed, and the loess is a distinctly glacial deposit, containing pal?olithic human remains and a pleistocene fauna, and embracing only a portion of the quaternary period. nor is it an isolated phenomenon confined to europe, but is found over the whole world wherever rivers have flowed from regions which were formerly buried under ice and snow. it is found in great force in the valleys of the yang-tse-kang and the mississippi, and sir charles lyell, referring to the fossil human bone found in it at natchez, says—"my reluctance in 1846 to regard the fossil human bone as of post-pliocene date arose, in part, from the reflection that the ancient loess of natchez is anterior in time to the whole modern delta of the mississippi. the table-land was, i believe, once a part of the original alluvial plain or delta of the great river before it was upraised. it has now risen more than 200 feet above its pristine level. after the upheaval, or during it, the mississippi 285 cut through the whole fluviatile formation, of which its bluffs are now formed, just as the rhine has in many parts of its valley excavated a passage through its ancient loess. if i was right in calculating that the present delta of the mississippi has acquired, as a minimum of time, more than 100,000 years for its growth, it would follow, if the claims of the natchez man to have coexisted with the mastodon are admitted, that north america was peopled more than a thousand centuries ago by the human race. but, even were that true, we could not presume, reasoning from ascertained geological data, the natchez bone was anterior in date to the antique flint haches of st. acheul."
human remains have since been found in the united states, both in the loess and in drifts, which are presumably older; but even if this were doubtful, the evidence would remain the same for the immense time required for such a deposit, and there is abundant proof in europe, that human implements, and even skulls and skeletons, have been found at considerable depths in the loess, along with remains of the mammoth and other extinct animals.
it must be remembered also, that the loess is only one part of the work due to glacial erosion. it is, in fact, only the deposit of the fine mud ground from the rocks by glaciers, and carried down further by rivers issuing from them than the coarser débris, which, as we have seen, cover 1,000,000 square miles to an average depth of fifty feet in north america alone. the volumes, therefore, of the loess and of the débris correspond, and tell the same story of enormous erosion requiring immense periods of time.
even in comparatively recent times striking proofs 286 of immense antiquity are afforded by the amounts of denudation and erosion which have taken place since the ice disappeared and the lands and seas assumed substantially their present contours and levels. i will give one instance which, although comparatively modern, will come home readily to most british readers. dr. evans in his ancient stone implements, referring to those found at bournemouth 100 feet above the present sea-level in the gravels of the old solent river, which then ran at that height, says—
"who, standing on the edge of the lofty cliff at bournemouth, and gazing over the wide expanse of waters between the present shore and a line connecting the needles on the one hand and the ballard-down foreland on the other, can fully comprehend how immensely remote was the epoch when what is now that vast bay was high and dry land, and a long range of chalk downs, 600 feet above the sea, bounded the horizon on the south? and yet this must have been the sight that met the eyes of those prim?val men who frequented that ancient river, which buried their handiworks in gravels that now cap the cliffs, and of the course of which so strange but indubitable a memorial subsists, in what has now become the solent sea."
and the same may be said of the still wider strait which separates england from france. no geologist could look either at the needles and ballard foreland, or at shakespeare's cliff and cape grisnez, without a conviction that the chalk ridge was once continuous, and has been worn away, inch by inch, by the very same process as is now going on. nor can the action of ice or river floods be evoked to accelerate the process, for 287 evidently it has throughout been a case of marine erosion. the only question is whether this dates back even into the later phases of the glacial period, for the opposite cliffs show no sign of having been either depressed beneath the sea or elevated above it, but rather appear to have stood at their present level since the erosion began. in any case it can only have occupied a comparatively short and recent phase of the glacial period, for there is abundant evidence that the british islands have been connected with the continent in comparatively recent times.
great, however, as is the antiquity shown by these comparatively modern instances, they sink into insignificance compared with that shown by a recent discovery, which i quote the more readily because it rests on the high authority of professor prestwich, who has been foremost among modern geologists in reducing the time required for the glacial period and for the existence of man. this is afforded by the upland gravels in kent and surrey, which are scattered over wide areas of the chalk downs and green-sand, at elevations far above existing valleys and watersheds, and which could only have been deposited before the present rivers began to run, and when the configuration of the country was altogether different. quite recently mr. harrison, a shopkeeper at ightham in kent, who is an ardent field-geologist, discovered pal?olithic implements, in considerable numbers and in various localities, up to an elevation of 750 feet above the sea level, in these gravels of the great southern drift. these discoveries, which have since been repeated by other observers, led professor prestwich to institute an exhaustive inquiry as to these upland drifts; and the 288 startling conclusion he arrives at is, that the oldest of them, or great southern drift, in which the implements are found, could only have come from a mountain range 2000 to 3000 feet high, which formerly ran from east to west in the line of the anticlinal axis which runs down the centre of the present weald of kent, between the north and south chalk-downs, and which has been since worn down to the present low forest-ridge by sub-a?rial denudation. the reasoning by which this inference is supported seems irresistible. the drift could not have been deposited by the present rivers or with the present configuration of the country, for it is found at levels 300 or 400 feet higher than the highest watersheds between the existing valleys. it consists not only of chalk flints, but to a great extent of cherts and sandstones, such as are found at present in the forest-ridge of the wealden and nowhere else. it must have been brought by water, for the gravels are to a considerable extent rounded and water-worn. this water must have run down-hill and with considerable velocity during floods, from the size of the rolled stones, and it must have come from the south, because the cherts and grits are only found there, and because the levels at which the gravels are found rise in that direction. by following these levels as far as the present surface extends, which is to the southern edge of the green-sand, it is easy to plot out what must have been the continuation of this rising gradient to the south, and what the elevation of the southern range in which these northward-flowing streams took their origin. prestwich has gone into the question in full detail, and his conclusion is, that the height of this wealden ridge must have been at least 2800 feet, or in other words, that 289 about 2000 feet must have disappeared by denudation. this is the more conclusive as prestwich is the highest authority, and he approached the subject with a bias for shortening rather than lengthening the periods commonly assigned for the glacial epoch and the antiquity of man.
the present average rate of denudation of continents has been approximately measured by calculating the amount of solid matter brought down by rivers. it varies a good deal according to the nature of the area drained, but the average is about one foot in 3000 years. at this rate the time required for the removal of 2000 feet of the wealden ridge would be no less than 6,000,000 years; but of course this would be no fair test, as denudation would be vastly more rapid than the present average rate, on hilly ranges and under glacial conditions of climate. it is enough to say that the time required must have been extremely great, and quite ample to fit in with the most extended time required by croll's theory of the varying eccentricity of the earth's orbit.
it is to be noted also, that prestwich pronounces part of this high level or southern drift to be older than the westleton pebble drift which forms part of the upper pliocene series in suffolk and norfolk, and which the professor has traced over many of our southern counties. if this conclusion is correct, it solves the problem of tertiary man by showing numerous pal?olithic implements in a stage older than an undoubted pliocene bed. the implements found in these high-level southern drifts are all of a very rude type, and the discovery is confirmed by similar implements having been found at corresponding elevations on 290 the chalk downs of hertfordshire and on the south downs.[10]
i will mention only one other instance, which shows that the new world confirms the conclusion as to the antiquity of the quaternary age. the auriferous gravels of california consist of an enormous mass of débris washed down by pre-glacial or early glacial rivers from the western slopes of the great coast range. during their deposition they became interstratified with lavas and tuffs from eruptions of volcanoes long since extinct, and finally covered by an immense flow of basalts, which formed a gently inclined plane from the sierra nevada to the pacific. this plane was attacked by the denudations of the existing river-courses, and cut down into a series of flat-topped hills, divided by steep ca?ons and by the valleys of the present great rivers. in one case, that of the colombia river, this denudation has been carried down to a depth of over 291 2000 feet, and the river flows between precipitous cliffs of this height. the present gold-mining is carried on mainly by shafts and tunnels driven through superficial gravels and sheets of basalts and tuffs, to the gravels of the pre-glacial rivers, which are brought down in great masses by hydraulic jets. in a great number of these cases stone implements of undoubted human origin have been found at great depths under several successive sheets of basalts, tuffs, and gravels. mr. skertchly, an eminent english geologist, who recently visited the district, says of these gravels, "whatever may be their absolute age from a geological standpoint, their immense antiquity historically is beyond question. the present great river system of the sacramento, joaquin, and other rivers has been established; ca?ons 2000 feet deep have been carried through lava, gravels, and into the bed rock; and the gravels, once the bed of large rivers, now cap hills 6000 feet high. there is ample ground for the belief that these gravels are of pliocene age, but the presence of objects of human formation invests them with a higher interest to the anthropologist than even to the geologist."
i will return to this subject more fully in a later chapter, when dealing with the question of the human remains found in these californian gravels.
those who wish to pursue the subject further will find abundant evidence in the works of lyell, geikie, evans, boyd dawkins, and other modern geologists, and a popular summary of it in my modern science and modern thought.
it is sufficient for my present purpose to have shown that even taking the quaternary period alone, geology shows that there is an abundant balance in the bank of 292 time to meet any demands that may be made upon it by any of the kindred sciences. but it is to those we must look for any chance of even an approximate measurement in years or centuries, for geology and pal?ontology only show immense periods, but give no certain information as to definite durations. the clue, if any, must be sought in croll's astronomical theory of the glacial period, which i now proceed to consider.
