Glacial epoch

“ When to this uniform testimony of the palæontological evidence we add the equally uniform absence of any indication of those ice-borne rocks, boulders, and drift, which are the constant and necessary accompaniment of every period of glaciation, and which must inevitably pervade all the marine deposits formed over a wide area so long as the state of glaciation continues, we are driven to the conclusion that the last glacial epoch of the northern hemisphere was exceptional, and was not preceded by numerous similar glacial epochs throughout Tertiary and Secondary time. ”

“ As two of these high excentricities greatly exceed that which caused our glacial epoch, while the third is almost equal to it and of longer duration, they seem to afford us the means of testing rival theories of the causes of glaciation. If, as Dr. Croll argues, high excentricity is the great and dominating agency in bringing on glacial epochs, geographical changes being subordinate, then there must have been glacial epochs of great severity at all these three periods ”

“ The records of the Glacial epoch are so plain and full that we are compelled to believe what otherwise would seem almost incredible, —that following the mild climate of the Tertiary came a succession of ages when ice fields, like that of Greenland, shrouded the northern parts of North America and Europe and extended far into temperate latitudes. ”

“ Many persons, even among scientific men, who have not given much attention to the question, look upon the whole subject of the glacial epoch as a geological theory made to explain certain phenomena which are otherwise a puzzle ”

“ Over against this marvel of a mild climate, luxuriant vegetation, and nearly equal days and nights within the Polar Circle, we may set that other wonder of the glacial or ice age—the time when the polar cold wandered beyond its bounds and came down into the temperate zone to stay, for how long we cannot tell; for very long indeed, no doubt, though not for as long as a world-building epoch. The Glacial age was only a portion of the age that came just before the human period. ”

“ Life, as Comus feared, was strangled with its waste fertility. Once, indeed, in the Permian Age, all over the temperate regions, north and south, we get passing indications of what seems very like a glacial epoch, partially comparable to that great glaciation on whose last fringe we still abide to-day. ”

“ According to the discoveries of Professor Wright and others, ancient stone implements have been found beneath the glacial drift, as well as the bones of animals whose descendants are now living, which goes to prove that man, with other species of fauna which now inhabit the earth, existed anterior to the glacial epoch. ”

“ If the cold of the glacial epoch came on slowly, if it was long before it reached its greatest intensity, and again if it abated gradually, we may expect to find the earliest and latest formed drift less barren of organic remains than that deposited during the coldest period. ”

“ Nor are such interglacial beds confined to northern and north-western Europe. In the Alpine Lands of the central and southern regions of our Continent they are equally well developed. Impressed by the growing strength of the evidence, it is no wonder that geologists, after a season of doubt, should at last agree in the conclusion that the glacial conditions of the Pleistocene period were interrupted by at least one protracted interglacial epoch. ”

“ Even the glacial epoch, during which vast ice sheets deposited drift over northeastern North America, must have been brief as well as recent, for many lofty mountains, such as the Rockies and the Alps, still bear the marks of great glaciers which then filled their valleys. ”

“ I have used it, however, for want of a better, and as an expression of convenience, always intending to express by the phrase "Glacial epoch" that section of geological time which was typically distinguished by the
prevalence of severe climatal conditions through a great part of the northern hemisphere, and during which those marine accumulations, in part truly sedimentary deposits, which have been called "Northern drift," were formed. ”

“ Even some portion of the palæolithic age, and of the more recent gravels and cave-earths may come into the same general period if they were formed when the glacial epoch was passing away. Now throughout all these ages we find no indication of change of species, and but little, comparatively, of migration. We thus get an erroneous idea of the permanence and stability of specific forms, due to the period immediately antecedent to our own being a period of exceptional permanence and stability as regards climatic and geographical conditions. ”

“ Throughout earlier Tertiary and Secondary times an equally high excentricity often occurred, but it never produced a glacial epoch, because the north temperate and polar areas had less high land, and were more freely open to the influx of warm oceanic currents. But wherever great plateaux with lofty mountains occurred in the temperate zone a considerable local glaciation might be produced, which would be specially intense during periods of high excentricity; and it is to such causes we must impute the indications of ice-action in the vicinity of the Alps during the Tertiary period. ”

“ If it is true that the Glacial epoch was one of elevation at the north—an elevation of the land much greater than the present—the change to the depressed condition of the Champlain epoch, when the sea stood from 1,500 to 1,800 feet higher on the coast of Greenland than it now does, must have been comparatively sudden ”

“ In any case the freehold of the cave was at last settled upon our early French artist. But the date of his occupancy is by no means recent; for since he lived there the long cold spell known as the Great Ice Age, or Glacial Epoch, has swept over the whole of Northern Europe, and swept before it the shivering descendants of my poor prehistoric old master. Now, how long ago was the Great Ice Age? As a rule, if you ask a geologist for a definite date, you will find him very chary of giving you a distinct answer. ”

“ By assuming such a succession of events we can more easily explain why there has not been a greater extermination of species, both terrestrial and aquatic, in polar and temperate regions, during the glacial epoch, and why so many species are common to pre-glacial and post-glacial times. ”

“ His special field of work, however, was the history of the glacial period in all its aspects, and as time went on he came to be recognised as the most thorough-going advocate of repeated glacial and interglacial epochs. ”

“ It is less important that an arbitrary definition should be accepted, than that the same meaning should be attached to technical terms in common use among geologists. In the interest of harmony and of a common understanding, and without the violation of any truth of science, we believe it would be well if the conception of a glacial epoch, as framed by those who are our leaders in position and in fact, were made the basis for our usage of the term. ”

“ Siberian Mammoths.—It will naturally be asked, whether some recent geological discoveries bringing evidence to light of a colder, or as it has been termed "glacial epoch," towards the close of the tertiary periods throughout the northern hemisphere, does not conflict with the theory above alluded to, of a warmer temperature having prevailed in the eras of the Eocene, Miocene, and Pliocene formations. In answer to this inquiry, it may certainly be affirmed, that an oscillation of climate has occurred in times immediately antecedent to the peopling of the earth by man ”

“ The astronomer also informs us that at a comparatively recent epoch the eccentricity of the earth’s orbit became very great. The conditions being favorable, it is not strange that a Glacial Age supervened.
We have been to considerable length in thus explaining the position of the scientific world in regard to the cause of the Glacial Age. Our reason for so doing is that this age is, we think, so connected with the Paleolithic Age of man, that it seems advisable to have a clear understanding in regard to it. What we have to say is neither new nor original. ”

“ But when the action of glaciers was studied and the recent occurrence of a glacial epoch demonstrated as a fact, many phenomena—such as moraines and other gravel deposits, boulder clay, erratic boulders, grooved and rounded rocks, and Alpine lake basins—were seen to be due to this altogether distinct cause. There was no breach of continuity, no sudden catastrophe; the cold period came on and passed away in the most gradual manner, and its effects often passed insensibly into those produced by denudation or upheaval ”

“ But before entering on the evidences which exist of the glacial era we shall glance at the picture presented by the animals of the period; the vegetable products we need not dwell on—it is, in fact, that of our own era, the flora of temperate regions in our own epoch. The same remark would apply to the animals, but for some signal exceptions. In this epoch Man appears, and some of the Mammals of the last epoch, but of larger dimensions, have long disappeared. ”

“ Professor Huxley called attention to this subject in a brief address to the London Ethnological Society in 1869. After stating the case, he presented the following queries and suggestions: “The Austro-Columbian fauna, as a whole, therefore, existed antecedently to the glacial epoch. ”

“ Glacial epochs are considered as exterminating influences and not as dispersing agencies, and on their cessation the areas over which they have exercised their icy and lifeless sway are again colonized from Nature's headquarters in the equatorial regions. ”

“ The climatic conditions are of course entirely different, and although the existence of an old glacial period may be suspected even in the torrid zone, the long ages that have elapsed since that remote epoch must have effaced nearly all trace of glaciers and moraines. ”

“ Now the geologist's spirit is so broken, that when the supposed discovery of glacial epochs in Silurian and Devonian time is announced, he hardly raises a dissenting voice, and appears to be resigned to the occurrence of glacial epochs at almost any time in the history of the earth. The theory of ancient climatic uniformity is definitely abandoned, and we must accept fluctuations of climate from the earliest geologic record all through the history of our planet. ”

“ But at times dryness may have contributed to the retreat of the ice even more than warmth, [Pg 26] and then the climate would have been continental, harsh, and extreme.
Even during epochs of glacial advance conditions in France and in the German zone must have been better than we should expect. Some kind of grazing or browsing pasturage must have been rich and abundant to support large animals like the reindeer or even the woolly mammoths characteristic of the second and third glacial epochs, which furnished abundant food for prehistoric hunters. ”

“ Now the Pleistocene was characterized by one of those periods of glacial cold which have swept over the earth—by one of those great winters which have so chilled the continents that few forms of life could survive them—and man comes in at the close of this cold period, in what is called the Post-glacial age. Some geologists, it is true, hold to an interglacial warm period, in which man is supposed to have existed, but the evidence of this is extremely slender and doubtful, and it carries back in any case human antiquity but a very little way. ”

“ For several hundred years all the great glaciers have receded, but we should not expect such recession to continue indefinitely. Geology furnishes abundant evidence that great changes took place in the climate of the earth during the prehistoric ages; that there were several glacial periods, the last occurring during pleistocene times, somewhere between twenty and fifty thousand years ago, and that there were intervals between the culminations of the Ice Ages of probably fifty thousand to one hundred thousand years. ”

“ The Pleistocene is regarded as being equivalent to what is known as the Glacial period. It began with the deployment of the ice-sheets which, proceeding from their centers of accumulation in British America, laid down in the East the Jerseyan drift and in the West the Nebraskan. The more the Glacial period is studied the more one becomes impressed with the significance of its physical effects on the northern hemisphere and with its influence on the vertebrate life. Doubtless its effects on the world in general are only beginning to be comprehended. ”

“ Glacialists may be ranged in two schools: those who believe that one or more phases of milder climatic conditions broke up the whole Glacial period into alternating epochs of glaciation and “deglaciation”; and those who believe that the intercalated deposits represent rather the localized recessional movements of the ice-sheets within one single period of glaciation. ”

“ They are, therefore, of no small importance in reference to the chronology of the glacial period, since they afford evidence of an assemblage of fossil shells with a proportion of between eight and nine in a hundred of extinct species occurring so far south as latitude 53 degrees north, and indicating so cold a climate as to imply that the glacial period commenced before the close of the Pliocene era. ”

“ Since most of the skeletal and cultural remains of man can now be definitely attributed to certain glacial, interglacial, or postglacial stages, vast interest attaches to the very difficult problem of the duration of the whole Ice Age and the relative duration of its various glacial and interglacial stages. ”