192 T. C. Chamherlin — Diversity of the Glacial Period. 



moraine and which for the present is to be associated in age 

 with the old glacial drift, though the two may not prove, upon 

 further examination, to be strictly contemporaneous. 



3. That after the formation of this older river deposit, 

 which took place at a low altitude and low gradient, theie was 

 an epoch of elevation and of erosion, during which the Dela- 

 ware cut its channel down to the depth of 200 to 300 feet 

 below the upper old terrace. 



4. That there followed a second incursion . of ice which 

 formed the Belvidere moraine, the over-wash of which ran 

 down into this previously formed gorge and filled it up to a 

 height of about 100 feet in the immediate vicinity of the 

 moraine, and to progressively less and less heights farther 

 down stream until at Trenton the height had declined to about 

 40 feet. 



If Professor Wright were correct in his correlation of the 

 terrace at Trenton, it would not affect, in any essential degree, 

 the history here given, because the other terraces within the 

 gorge above, some of them in the immediate vicinity of the 

 moraine and in immediate connection with it, constitute the 

 essential part of the evidence. I do not think that any geolo- 

 gist, at all expert in these lines, can entertain any doubt as to 

 contemporaneity of these terraces with the moraine, or that 

 the gorge was formed antecedent to the moraine, or that the 

 higher terraces, capped with the old gravels and clays, were 

 formed earlier than the gorge ; and I am surprised that any- 

 one professing familiarity with drift phenomena, should ques- 

 tion the markedly superior age of the old drift. 



The phenomena on the Delaware, therefore, taken in con- 

 nection with those of the St. Lawrence and Champlain Val- 

 leys, seem to admit of no rational interpretation that does not 

 involve two depressions and an intermediate stage of eleva- 

 tion. The duration of the elevation has as its minimum 

 measure the cutting of the river gorge and the high-gradient 

 glaciation beginning with the Belvidere moraine and embrac- 

 ing several subsequent episodes of undetermined length. I 

 conceive that there may be differences of judgment as to how 

 much divisional value such orographic stages and such alterna- 

 tions of action and such evidences of aging may be entitled to ; 

 but that here are tangible divisions of the glacial history of the 

 region that are of fundamental importance in the interpreta- 

 of the deposits and in the determination of the glacial rela- 

 tions of supposed art relics, does not seem to me to admit of 

 question. 



The phenomena on the Susquehanna are, so far as known, 

 very closely similar to those upon the Delaware, but they have 

 been much less fully worked out and may be passed over. 



