194 



CAPE COD GEOLOGY 



In West Tisbury the moraine reaches its best development in the Indian 

 Hill region. Beyond this it is interrupted by James Pond and the valley south- 

 east of it. 



In the region about Chappaquonsett Pond the direction of the morainal 

 belt was changed by the interlobate re-entrant in the ice front, and there the 

 character of the topography and the nature of the deposits are somewhat 

 modified. Between Lagoon Pond and the State road on the west there are 

 sandy morainal deposits but no sharp ridges. Similar deposits are seen on the 

 east side of Lagoon Pond and farther southeast, where the morainal area grows 

 narrower, especially near Sengekontacket Pond. (See Plate 17, fig. 1.) Expos- 

 ures are scarce in this whole region, and the till cannot easily be separated from 

 the bedded deposits. The difference in the topography and the morainal de- 

 posits here and those in the western area is probably due to a re-advance of the 

 ice after the moraine had been formed. The morainal deposits of the Cape Cod 

 Bay lobe have been described as "kame-moraines." The ice that moved over 

 the moraine modified the form of the ridges and converted much of the surface 

 material to a sandy till, which overlies the morainal deposits that have the 

 bedding of kames. 



The moraine continues beyond Sengekontacket Pond but is interrupted 

 at Edgartown by the narrow strait that connects Edgartown Harbor and 

 Katama Bay. On Chappaquiddick the moraine grows much broader and 

 finally it becomes lower and disappears under the sea at the east side of the 

 island. 



Otjtwash Deposits 



The outwash deposits of the Wisconsin stage lie in the great plain south 

 of the Nantucket moraine. (See Plate 15, fig. 2). The material of this out- 

 wash varies from coarse gravel containing rather large pebbles to sand, and it 

 is coarsest along its northern boundary. In the southern area the upper layers 

 are coarser than the lower ones. No boulders are found in the outwash gravel, 

 which contains pebbles of many kinds of rock. Exposures of the outwash are 

 very scarce, for its deposits are flat and the area it occupies has not been in- 

 habited by man. The beds of outwash seen in the banks of the ponds in the 

 southern part of the plain appear to lie nearly horizontal, although they prob- 

 ably dip gently to the south. 



The material of the outwash was brought to this region by the ice, from 

 which it was carried out and deposited by glacial streams. Most of these streams 

 issued from the base of the ice and therefore contained a larger proportion of 



