The glacial period also, which in the Old World affords such a clear demarcation between Tertiary and Recent ages, and such manifest proofs of two great glaciations with a long inter-glacial period, presents different conditions in America, where the ice-caps radiated from different centres, and extended further south and over wider areas. There is no proof whether the great cold set in sooner or later, and whether the elevations and depressions of land synchronized with those of Europe. The evidence for a long inter-glacial period is by no means so clear, and the best American geologists differ respecting it. And above all, the glacial period seems to have lasted longer, and the time required for post-glacial or recent denudation, and erosion of river-gorges, to be less than is required to account for post-glacial phenomena on this side of the Atlantic. The evidence, therefore, from the New World, though conclusive as to the existence of man from an immense antiquity, can hardly be accepted as equally so in an attempt to prove that antiquity to be Tertiary in the sense of identifying it with specific European formations. With this reservation I proceed to give a short account of this evidence as bearing on the question of the oldest proofs of man's existence. The first step or proof of the presence of man in the Quaternary deposits which correspond with the oldest river-drifts of Europe, has only been made quite recently. Mr. Abbott was the first to discover such implements of the usual palæolithic type in Quaternary gravels of the river Delaware, near Trenton in New Jersey, and since then they have been frequently found, as described by Dr. Wright in his recently-published _Ice Age in America_, in Ohio, Illinois, and other States, in the old gravels of rivers which carried the drainage of the great lake district to the Hudson and the Mississippi, before the present line of drainage was established by the Falls of Niagara and the St. Lawrence. So far the evidence merely confirms that drawn from similar finds in the Old World of the existence of man in the early glacial or Quaternary times, already widely diffused, and everywhere in a similar condition of primitive savagery, and chipping his rude stone implements into the same forms. But if we cross the Rocky Mountains into California, we find evidence which apparently carries us further back and raises new questions.