186 



CAPE COD GEOLOGY 



very near the surface. It is seen in several exposures along the State road. (See 

 Plate 24.) Along the north side of Gay Head the till is covered by more gravel 

 than elsewhere. 



Along the northwest shore of the main island there are many exposures 

 of Montauk till. In the Norton Point cliffs it is not well exposed, although it is 

 seen at some places. It is exposed immediately west of Paul Point, and at Cedar 

 Tree Neck there is a small cliff composed entirely of the Montauk till which, 

 however, presents a nearly vertical face, without the typical erosion forms. 

 This peculiarity is due to the fact that no streams flow over the cliff, the rainfall 

 from the cliff flowing down the slope to the small pond back of the shore. The 

 cliff is therefore eroded only by the waves. From Cedar Tree Neck to Cape 

 Higgon practically all the bluffs expose Montauk beds. At Cape Higgon itself 

 very little is seen, but in the cliffs northeast of Roaring Brook the till is seen 

 again above the Herod gravel and Gardiners clay. From Roaring Brook to 

 Menemsha the Montauk till appears in places, especially west of Prospect Hill. 

 For the details of the occurrence of the Montauk till along the shore, reference 

 should be made to the diagrams showing sections of the cliffs. 



Age. — The stratigraphic position of the Manhasset formation, of which 

 the Montauk till is the middle member, can clearly be established as post-Jacob 

 and pre-Vineyard. It overlies the Jacob sand at many places, yet it was subject 

 to extensive erosion during the Vineyard interval. There is no evidence of an 

 ice advance between the Montauk till and the Wisconsin moraine. The erosion 

 during the Montauk interval was deep and must have been rather long as 

 compared with the post-glacial erosion of the beds of clay and sand of the 

 island by streams and rainfall. The Manhasset and its included bed of Montauk 

 till are clearly the products of a glacial stage prior to the Wisconsin stage and 

 separated from it by a long interglacial stage of fluvial conditions. The Man- 

 hasset may be the eastern representative of the Illinoian drift. The Man- 

 hasset and its intercalated bed of Montauk till constitute the thickest glacial 

 deposit on Marthas Vineyard, agreeing in thickness with the Illinoian drift of 

 the Mississippi valley, which is somewhat greater than that of the Wisconsin. 



Hempstead Gravel Member 

 Name. — "After the Montauk invasion and its attendant [ice] erosion, de- 

 position, and folding, the ice retreated from Long Island and a series of gravels 

 were laid down, doubtless derived from the ice, which appears to have lingered 

 in the vicinity. For these gravels, which represent the uppermost of the three 



