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Updated: June 11, 2025
The first, the Pleistocene or Glacial epoch, is marked off from the Tertiary by the occupation of the northern parts of North America and Europe by vast ice sheets; the second, the Recent epoch, began with the disappearance of the ice sheets from these continents, and merges into the present time.
It is quite easy to fancy a state of society, vastly different from ours, existing in some unknown place like heaven; it is much more difficult to realise as a fact that the order of things with which we are familiar has so little stability that our actual descendants may be born into a world as different from ours as ours is from that of our ancestors of the pleistocene age.
In other words, if we suppose that the axis of the earth does not consistently point in one direction that the great ball does not always present the same average angle in relation to the sun the poles will not always be where they are at present, and the Pleistocene Ice-Age may represent a time when the north pole was in the latitude of North Europe and North America.
This opinion had to be abandoned. We have no trace whatever of such a constant shifting of the polar regions as it supposes, and, especially, we have no trace that the warm zone correspondingly shifted in the Pleistocene. A much more elaborate theory was advanced by Dr. Croll, and is still entertained by many.
One is the rise of the land; the other is the thinning of the atmosphere. These are closely related agencies, and we found them acting in conjunction to bring about the Permian Ice-Age. Do we find them at work in the Pleistocene? It is not disputed that there was a very considerable upheaval of the land, especially in Europe and North America, at the end of the Tertiary Era.
In that country they have probably not been confined simply to subsidence, but have comprised oscillations in the level of the land, by which marine shells of the Pleistocene period have been raised some 10 feet or more above the level of the sea.
It has taken the geologist a long time to work out and clear up and confirm this conception of the great continental glacier which in Pleistocene times covered so large a part of the northern hemisphere. It is now as well established as any event in the remote past well can be. In Alaska, and in the Swiss Alps, one may see the ice doing exactly what the Pleistocene ice-sheet did over this country.
They all without exception have a lower jaw with the teeth of the exact number and grouping which you may see in a sheep's lower jaw. We know hundreds of them, both living and fossil, many from the Pleistocene, others from Pliocene deposits, and even from the still older Miocene, but all keep to the one pattern of lower jaw and lower jaw teeth.
If the lower flattened cone of Tiniere be referred in great part to the age of the oldest lake-dwellings, the higher one might perhaps correspond with the Pleistocene period of St.
The Pleistocene epoch consisted, therefore, of several glacial stages, during each of which the ice advanced far southward, together with the intervening interglacial stages when, under a milder climate, the ice melted back toward its sources or wholly disappeared.
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