358 Geology of Long Island. 



In view of the fact that we have nowhere else any good evidence 

 of a change of sea level amounting to 200 feet in the vicinity of New 

 York during the Glacial epoch, we can only account for the high 

 elevation of some of these fossils by supposiug that they, with 

 their containing beds, have been raised to their present position 

 by glacial action in the manner I shall describe. 



Of the physical conditions under which the presumed Creta- 

 ceous and Tertiary beds were deposited, we know nothing ; 

 though it is reasonable to conclude that they consist of the debris 

 of New York and New England rocks carried down from the 

 highlands and deposited along the coast by rivers .or by other 

 agencies of transportation. The overlying deposits of strati- 

 fied gravel, sand and clay, part of which, as before stated, are 

 equivalent to the "yellow drift" of New Jersey, are also difficult 

 to account for. They consist largely of transported material 

 from older beds, and by their structure indicate that they have 

 been formed by swift currents which carried along and deposited 

 coarse and fine material mingled together. Their fossils, so far 

 as we know, exclude them from the Tertiary, and they underlie 

 the drift un conformably, although by definition the Glacial pe- 

 riod begins the Quaternary age. 



If, however, we assume in the Quaternary a succession of 

 glacial epochs, or alternate periods of advance and retreat of 

 the ice-sheet, as suggested by Croll's theory, we can explain 

 the origin of the beds in question by supposing that during 

 the epoch of glaciation immediately preceding their deposi- 

 tion, the ice-sheet did not reach so far south, while the floods of 

 of the succeeding warmer epoch modified and spread over the 

 sea-bottom the drift thus formed. 



In order to appreciate more exactly the relations of these Post- 

 pliocene beds to the glacial drift, it will be necessary to consider 

 some very interesting phenomena. Along the north shore of 

 Long Island from Flushing to Orient Point, are exhibited most 

 striking evidences of glacial action. We find the stratified gra- 

 vels, sands and clays upheaved by the lateral pressure of the ice- 

 sheet and thrown into a series of marked folds at right angles 

 to the line of glacial advance, which, judging from the grooves 

 and striae on the rocks of New York and Connecticut, was about 

 S. 30° E. The glacier having thus crumpled and folded the un- 



