MONTAUK DRIFT 383 



boulders present. It takes its name from Montauk point, Long island, 

 where it is typically developed (plate 66, figure 2). 



Conditions of deposition. — So far as can be judged from the character 

 of the Herod deposits, the accumulation was entirely submarine. Ante- 

 dating the beginning of Montauk deposition, however, there was an up- 

 lift, bringing the land in the vicinity of Fishers island somewhat nearer 

 to the present level, although, as indicated by the occurrence of the Mon- 

 tauk deposits below sealevel, except when brought up by folding, the 

 level was still lower than that at present existing. The ice-front, which 

 had been remote at the beginning of the deposition of the Jacob sands, 

 had approached nearer during the deposition of the Herod gravels, and 

 at the beginning of the Montauk substage actually invaded the area, 

 passing in its maximum advance over Fishers island and southward to 

 a point beyond Block island. The accumulation seems to have taken 

 place beneath the ice-sheet itself in case of the more till-like deposits, 

 where stratification is absent, while in the case of the semi-stratified 

 materials it probably occurred outside but immediately in front of the 

 margin. The thin beds of true gravels, which are occasionally inter- 

 bedded with the more till-like deposits, probably represent temporary 

 retreats of the ice-margin to points at some distance from the localities 

 of accumulation. 



Character and occurrence of the Montauk drift. — The general features 

 of the Montauk drift have already been outlined and the normal type 

 illustrated in* plate 66, figure 2. On Fishers island it is of somewhat 

 different character, although the exposures are typical of certain well 

 defined phases near the type locality. The drift has only been recog- 

 nized above sealevel at two points : (1) At the West Harbor exposures 

 and (2) in the bluff three-quarters of a mile northeast of the north end of 

 Isabella beach. The " boulders " reported in the Ferguson well probably 

 belong to this formation. 



At the West Harbor exposure (figure 10) the Montauk drift is proba- 

 bly represented by the heavy bed of till resting unconformably on the 

 upturned and eroded edges of the Jacob sands and Herod gravels. This 

 unconformity is believed to be the result of essentially contemporaneous 

 erosion by the same ice-sheet that laid down the drift. On Long island } 

 where many more exposures are to be seen, there are similar evidences 

 of slight deposition of till at this time, but the main epoch of folding was 

 of a later date. 



At the second of the localities mentioned the exposures show a series 

 of beds of clayey sand alternating with beds of pebbles about the size of 

 a hen's egg occurring in a matrix of clay or clayey sand. Both sand and 

 gravel show the peculiar mixture of coarse grains or pebbles with fine 



LII— Bull. Geol. Soc. Am., Vol. 16, 1904 



