1896.] KEW YORK ACADEMY OF SCIENCES. 15 



that I have been able to find in relation to the Island's geology. 

 The grand development of glacial phenomena seemed to act as 

 a damper upon more minute investigation and apparently served 

 to discourage the study of details. 



I take it for granted, from what others have written, that there 

 is no question on the part of observers in regard to the Island 

 being an isolated portion of the southern terminal moraine, 

 which extends westward from Montauk Point and eastward 

 through Martha's Vineyard and Nantucket. In general we ma}^ 

 say that it closely resembles Montauk Point, only on a much 

 grander scale. This is notably the case around the eastern, 

 southern and western shores, from Old Harbor Point to Grace 

 Point, where the ocean has eaten into the hills, leaving bold 

 bluffs, in places more than a hundred feet high, with fine sections 

 exposed for study. To a lesser extent this is also true of Clay 

 Head near the northern end. 



Two days were spent in examining the shore line. Half a day 

 from Old Harbor Point to Southeast Lighthouse ; half a day 

 from the latter to Black Rock Point ; half a day from thence to 

 Grace Point and the remainder of the time at Clay Head. 



The sections exposed between Old Harbor Point and Grace 

 Point are practically alike and probabl}^ represent the prevail- 

 ing structure and composition of the hills throughout the 

 southern portion of the Island. There is a core or base of dark 

 sandy clay, much contorted but with a prevailing dip towards 

 the northwest, with gravel and bowlder till resting upon the 

 eroded and crumpled surface. These clays are probably of 

 the same age as those at Montauk Point, although no 

 paleontologic evidence was discovered. Confirmatory evidence 

 in other directions was however obtained. 



Just east of Black Rock Point our attention was attracted by 

 an irregular mass of clay forming part of the heterogeneous ma- 

 terial above the dark sandy cla}'^ at the base. It was variegated 

 in color, containing streaks of red, yellow, white and black, and 

 was much finer and more plastic than that below.* We at once 

 agreed that it must be Cretaceous, if lithologic similarit}^ 

 amounted to anything, and further, that it had been carried for- 

 ward en masse in the drift, as is so commonly the case on Long 

 Island and Staten Island. This indicated the presence of a Cre- 

 taceous clay outcrop northward, where it would normally be- 

 long if the sandy c\a.y in place in the bluffs represented either 

 the Tertiary or the Cretaceous clay marl horizon. 



We hardlj' expected that this theoretical outcrop would be 

 found on the Island, but upon reaching the bluff at Grace Point 



* This is probably the outcrop mentioned by Upham, previously cited. 



