386 M. L. FULLER — GEOLOGY OF FISHERS ISLAND 



The maximum advance occurred in the early part of the stage, the 

 ice reaching as far south as Block island, but later it drew back to Fishers 

 island, or perhaps beyond, where it halted during the building of the 

 morainal deposits. The recession was a relatively rapid one, the inner 

 moraine and its attendant outwash plain being built up, as shown in 

 eastern Long island, before the ice-blocks left by the retreat had time to 

 melt. 



The deposits of the Wisconsin stage on Fishers island consist mainly 

 of till, which varies somewhat in character, according to the derivation 

 of the material. When from the island it is buff and sandy, with few 

 boulders, representing, in fact, simply the reworked parts of the under- 

 lying materials, especially the Herod gravels. At other points the till is 

 composed largely of granitic materials brought from the mainland. In 

 such till clay is relatively abundant, and, together with the granitic frag- 

 ments, gives the till its grayish color. Boulders are numerous and often 

 of considerable size. 



The best development of till is in the western part of the island, 

 especially west of West harbor. In this region the low bluffs at many 

 points show a till very full of boulders, while the kettle-pitted uplands 

 and the morainic knobs point to more than the ordinary amounts of 

 Wisconsin drift. In the eastern part of the island the Wisconsin drift 

 is thinner, the sands and gravels of the Herod formation being but thinly 

 covered. Sometimes the Wisconsin drift is limited to a few scattered 

 boulders. No stratified materials of this stage are recognized, and, while 

 a few may have been overlooked, it is certain there is no extensive devel- 

 opment of such deposits on the island. 



Recent history. — There is little record on the island of any post- Wis- 

 consin events. There has been no stream erosion, and the cutting of the 

 bluffs has probably not been extensive. Some small spits have been 

 built, and there has been a slight accumulation of marsh and swamp 

 deposits in spots ; but, in the main, there has been little change in the 

 island since the ice left it, other than a possible submergence of a few 

 feet. Even of this, however, no local evidence was found, although from 

 studies on Long island and at points to the east of Fishers island it 

 appears that a subsidence of perhaps 10 feet has occurred since the 

 retreat of the ice. 



Correlations 



rela tion of gardiner cla y, jacob sand, and herod gra vel to " sankaty 

 beds" (woodworth) of marthas vineyard and nantucket 



The term " Sankaty beds " was proposed by J. B. Woodworth f 



*The diversity of the glacial period on Long island. Jour, of Geol., vol. xi, 1903, pp. 763-776. 

 f Glacial brick clays of Rhode Island and southeastern Massachusetts. U. S. Geol. Survey, Sev- 

 enteenth Ann. Rept., pt. i, p. 977. 



