T. C. Chamberlin — Diversity of the Glacial Period. 191 



waters of the Delaware, and after the land had nearly resumed 

 its present relations of level, if indeed, it had not risen north- 

 ward to a still greater height."* ISTow it is incontestable that 

 it was after the ice had retired from the head waters of the 

 Delaware, that the depression occurred during which the 

 marine deposits of Montreal and the Champlain region were 

 laid down. Professor Wright also states that between the 

 deposit of the Philadelphia brick-clay and that of the Trenton 

 gravel, there was a " long interval."f We, therefore, have 

 Professor Wright referring to the Champlain depression 

 deposits that were laid down long anterior to the Trenton 

 gravels, which, in turn, were deposited at a time of elevation 

 which, in its turn, was demonstrably early than the Cham- 

 plain deposits. To refer the slackwater deposits of the Dela- 

 ware and the marine deposits of the Champlain Valley to the 

 same depression, and yet put between them a "long interval" 

 and a period of elevation, is a characteristic instance of the 

 self-destrnctive interpretations to which the old doctrine of 

 unity naturally invites. 



Besides the evident error of confounding two depressions, 

 separated from each other by the acknowledged interval occu- 

 pied in the erosion of the gorge of the Delaware and by the 

 intervention of an elevation comparable to the present, there 

 is a specific error in Professor Wright's correlations. He 

 makes the well-known gravel terrace at Trenton the correla- 

 tive of a terrace of less than half its height at Yardville, a few 

 miles above, overlooking the fact that terraces of the same 

 nature and gradually rising altitudes occur at short intervals 

 all the way from Trenton to the Belvidere moraine. There 

 they join the moraine in the characteristic fashion of moraine- 

 headed terraces with which students of the high-gradient 

 terminal moraines have become familiar. That this connec- 

 tion is clear and demonstrative is the judgment of at least 

 five geologists who have studied the formations. 



It is altogether probable that a complete analysis of the 

 drift formations of the Delaware will develop some additional 

 factors, and possibly extend its history, but the following feat- 

 ures I think may be accepted as demonstrative : 



1. That there was an earlier invasion of the ice which 

 reached at least a dozen miles south of the Belvidere moraine. 

 For present purposes it does not matter at all whether it in- 

 cluded the High Bridge and Pattenburg deposits or not, nor 

 whether the more distant drift is glacial or glacio-natant. 



2. That there is an older fluvial deposit (the Philadelphia 

 brick-clay) which is likewise much older than the Belvidere 



* " Man and the Glacial Period," p. 261. 

 f " Man and the Glacial Period." p. 257. 



