Page:The Journal of geology (IA journalofgeology11893univ).pdf/216

must be judged, have been widely discussed. These criteria are not new to the specialists who had earlier defined and used them. But not until now had it been so clear to so large an audience that the evidence concerning man's antiquity is primarily geological, and more than this, that it involves some of the nicest and most particular questions with which geologists have to deal.

The article of Mr. Leverett in this number gives occasion to invite attention to certain errors that still linger in the literature of the glacial period, and that are occasionally supplemented by new ones of like nature. They grow out of the failure to distinguish between the Champlain depression and the earlier depression during which the main silts of the Mississippi Valley were deposited. A very large mass of evidence has been presented by different investigators under different auspices during the past decade that seems to us to have completely demonstrated a stage of elevation between the time of the main silt depositions associated with the outer tract of drift in the interior basin, and the time of the low-altitude formations of St. Lawrence basin of which the deposits of the Champlain valley are the type. This stage of elevation embraced some of the most important events of the glacial period. The two stages of depression, we think, have thus been proved to be altogether distinct. In our judgment they were separated by a long interval of time, but it is not important to insist upon this in this connection. The evidences of this elevation between the two stages of depression embrace practically all the great glacial gravel trains of high gradient that are found south of the St. Lawrence basin. The nature and slope of these give clear testimony to the attitude of the land at the time of their formation. It is not asserted that there were not similar trains connected with the early stages of the earlier invasion of the ice, but the evidence on this point is as yet very scant. It certainly does not embrace the well-known high-gradient valley deposits of the interior, for these lie in valleys cut in the earlier drift and are connected with moraines that lie