Page:The Journal of geology (IA journalofgeology11893univers).pdf/433

later episodes (or the earlier episodes) exclusively and those who have studied both. To have studied the Hudson River beds, east and west, is an inadequate preparation for deciding whether they are to be placed in a separate epoch from the Trenton beds or not. Both the Hudson River beds and the Trenton beds should be studied in regions where both are well displayed. So of the drift deposits. Classified on the basis of the formational distribution of critical studies, the true generalization falls easily into form, viz., those who have studied the formations of one epoch believe in one epoch; those who have studied the formations of more than one epoch, believe in more than one epoch.

The special individual opinion upon which Professor Dana lays stress ceases to have significance, or rather has its significance reversed, when it is observed that the studies on which it is based (most admirable in extent and in quality) fall almost exclusively within zones referred, by common consent, to a single, late, relatively brief glacial epoch.

Respecting the reference of the differences between the drift of the east and of the west to meteorological causes there is room here only for inviting attention to the pregnant fact that the greatest southward extension of the drift is found where the present meteorological and topographical conditions are least favorable. The drift of the interior reaches south of 38° latitude, that of New England only a little south of 41°, a difference that equals about three-fourths of the extent of New England in latitude, exclusive of Maine. The inferiority of the drift of New England in extent, in massiveness, and in series development is the feature that calls for explanation in adverse conditions rather than the magnificent deployment of the glacial series on the plains of the interior.