CAPE COD GEOLOGY 



165 



clay and the Jameco gravel or of the boulder beds at that horizon in certain 

 sections. If the strata were distorted by pushing or dragging at the margin of 

 an ice sheet advancing from the north, the earliest competent ice advance 

 would have shoved the beds into a position of approximate equilibrium, so that 

 subsequent ice advances would leave no marked signs of their work. This ap- 

 pears to be true, and we are therefore led to believe that the ice advance of the 

 Jameco stage was the greatest that had taken place since the beginning of 

 Pleistocene time, but the nature of the folding alone does not indicate that 

 this ice advance was less vigorous than those which followed it. In the typical 

 section of the beds that were folded and overthrust at this time, both on Block 

 Island and Marthas Vineyard, the overthrust moved from the landward side 

 toward the sea. The deployment to the southwest, over the Gay Head section, 

 as compared with the overthrust to the southeast, over Marthas Vineyard east 

 of Menemsha Creek, indicates the existence of a small lobe or tongue that 

 pushed southward through the depression occupied by Menemsha Pond. This 

 depression, along with the rest of the island, has been an area of deposition and 

 erosion, but probably its original cause lies in its axial position in reference 

 to the ice push at this time. 



The deposition of the Gardiners clay about what appear to have been 

 islands or shoals of Cretaceous clay has already been noted. The precise char- 

 acter of the topography impressed upon the coastal plain by the ice sheet is 

 not known. Probably much of the inequality of the surface is a result of differ- 

 ences in the resistance of the beds to crowding and dislocation. The surface of 

 the deformed mass was highest where the clays permitted packing, which 

 foreshortened the section and consequently forced the moving ice to ride over 

 the rising obstruction. Whether this action took place beneath sea level or 

 above cannot easily be determined. The general character of the Jameco gravel 

 suggests shallow water or the action of streams on a plain above sea level. The 

 immediately succeeding Gardiners clay was evidently laid down during a period 

 of submergence. 



Nashaquitsa Cliffs. (Plate 23, fig. 1) 



Weyquosque formation. — At the east end of the Nashaquitsa cliffs the pre- 

 Gardiners beds are exposed, although the complete series seen at Gay Head 

 is not shown. The east end of these cliffs consists of Cretaceous sand and clay, 

 against which abut the older Pleistocene beds. (Fig. 11.) 



The lowest Pleistocene bed grades from brown gravel up into a dark sand, 



