PLEISTOCENE GEOLOGY OF NASSAU CO. AND BOROUGH OF QUEENS 653 



This fanning of the ice sheet to the eastward on the east side of 

 the lower Hudson and to the westward on the west side is consistent 

 with the form of the moraine across the mouth of the river. The 

 axis of the lobe thus indicated has been fixed by Salisbury on the 

 west side of the Palisade trap ridge.^ 



From wliat has been stated, it would appear that the western end 

 of Long Island is occupied by a moraine and a contemporaneous 

 outwash plain built along the margin of the ice sheet, when it had, 

 in this region adjacent to the mouth of the Hudson, ]3U8hed a lobate 

 mass somewhat farther south than the limit attained by an earlier 

 stand of the ice front, marked eastward by the outer moraine from 

 near Roslyn to JSTantucket ; that the frontal plain in this district rises 

 to slightly different lev^els against the front of the moraine, a feature 

 which is constructional and not due to post-glacial warping ; and that 

 the front of the moraine as a whole presents no decisive evidence 

 of having been subjected to marine action above the present level 

 of the sea. 



With this statement of the observations bearing on the marine 

 limit at the time of the last ice invasion, it is necessary to return to 

 the later ice phenomena exhibited in connection with the Port 

 Washington stage of the' retreat. 



Port Washington glacial lake 



It has already been pointed out that the last evidence of the pres- 

 ence of the ice sheet on the area covered by the Oyster bay quad- 

 rangle is found in a well defined delta and attendant ice-laid deposits 

 occupying the semicircular tip of Mannasset neck. The phenomena 

 indicatinoj a halt of the ice front as^ainst this headland for a brief 

 time subsequent to the retreat from the inner moraine at Roslyn are 

 very clear. The conclusion having been reached that the area has 

 not been submerged to the depth of 80 feet since the beginning of 

 the deposition of moraines in this part of the island, it seems neces- 

 sary to further examine the region to determine the possibility of 

 this delta having been built in a temporary glacial lake. 



To the north and west of Port Washington occur a number of 

 gravel and sand pits opened in a characteristic glacial delta, whose 



» Salisbury, R. D. N. J. geol. sur. An. rep't state geol. for 1893. 1894. p. 161. 



