260 



CAPE COD GEOLOGY 



are characteristic of the Mont auk till rather than the Gar diners clay as known 

 on Marthas Vineyard, No Mans Land, Block Island, and Long Island. The 

 clays about Pleasant Bay may not lie at the same horizon as those seen about 

 Barnstable, but are probably part of the same deposit that underlies the south- 

 ern part of Cape Cod at about sea level. 



In the bluff on the south side of the entrance to Nauset Harbor there is 

 an outcrop of till or clay containing striated stones and underlain by gravel 

 and sand. This outcrop lies within the boulder-strewn area of the Falmouth 

 moraine, but the bed of till appears to be in the older Pleistocene below the 

 surface moraine. There is also a small exposure of stony clay in the low bluff 

 at the Nauset Beach coast guard station. This bed is only 3 or 4 feet thick and 

 overlies about 6 feet of brown clay. The entire section at this point appears to 

 be a part of the Eastham plain, and is possibly newer than the section at the 

 entrance of Nauset Harbor. Deposits of sand, gravel, clay, and pebbly till were 

 probably laid down at all the glacial stages along the ice front, which probably 

 advanced at times over its washed deposits and then retreated so as to produce 

 alternations of stratified and unstratified deposits. The two sections described 

 show that there are several beds of true stony clay till on the Cape and that 

 their positions in the older Pleistocene succession can be determined only where 

 the beds of clay or till are very thick and extensive. 



Hempstead Gravel Member (?) 



Beds of gravel overlie the blue clay in the southern part of Cape Cod in 

 a position comparable with that of the Hempstead gravel, which lies upon the 

 Montauk till in the islands. If the clay in the southern part of the Cape is the 

 Gardiners clay the gravel and sand beneath the morainal outwash correspond 

 in position to the Herod gravel, which lies beneath the Montauk tills. 



Summary 



The beds of gravel and sand that lie above the clay are evidently older than the 

 Wisconsin outwash gravel in the southern part of the Cape and represent the 

 Manhasset formation, which is composed of the Herod gravel member below, the 

 Montauk till in the middle, and the Hempstead gravel member above. All three 

 of these members are found on Cape Cod. In the plain on the south side of the 

 Cape these beds of gravel and sand, where they are not covered with the out- 

 wash from the Falmouth moraine, show traces of erosion channels made by 

 streams prior to the Wisconsin stage. 



