264 



CAPE COD GEOLOGY 



WISCONSIN GLACIAL DEPOSITS 



The deposits of the Wisconsin stage of glaciation on Cape Cod consist of 

 certain beds of sand and gravel, and probably also some of till, which were laid 

 down along the south side of the Cape during the first advance of the ice to 

 Nantucket and during times when stagnant masses of that sheet of ice were 

 melting, as late as the second advance, which reached only the position of the 

 morainal ridge that skirts the southern arm of the Cape. Practically all the 

 boulders, gravel, sand, and clay in the high plains and morainal mounds from 

 Woods Hole northward past Buzzards Bay and thence eastward to Orleans 

 pertain to the second and last ice invasion. These two distinct groups of Wis- 

 consin deposits are described below. 



NANTUCKET SUBSTAGE 



The terminal moraine of the Nantucket substage lay some 30 miles south 

 of the Falmouth moraine. The deposits and the topographic features on Cape 

 Cod pertaining to the Nantucket substage are widely spread south of the Fal- 

 mouth moraine. 



Practically all the kettle holes and glacial lakes of that region, even those 

 that lie within the Falmouth moraine, represent the sites of blocks of ice formed 

 while the stagnant ice of the Nantucket substage was melting. The block of 

 ice that occupied the site of Great Pond, in the town of Barnstable, must at 

 first have risen high enough above the surrounding surface to supply by its 

 melting not only a considerable stream, which flowed from its southern border, 

 but fans of gravel and sand that were built out from its side. 1 



One has only to fill these depressions in imagination with large berg-like 

 masses of ice, which were more or less charged with stones and sand and which 

 rose above the level of the plains of that part of the Cape, to gain a vivid picture 

 of the landscape at the time the ice sheet of the second or Falmouth substage 

 yet lay against the northern slope of its terminal moraine. 



These ice masses lay in chains and groups that had rather well-defined 

 directions. A remarkable chain extended across the plains in Barnstable from 

 Pondsville southward to Great Bay, east of Cotuit, a region in which the back 

 bays of the coast are ice-block holes. The northernmost depressions in this 

 chain, known as the Cotuit ponds, are separated by transverse ridges supple- 

 mented by bars thrown up by the waves on the lakelets. Here a large mass was 



1 Woodwdrth, J. B., Some glacial wash plains of southern New England, Bull. Essex Inst., 29, 1897 

 (issued in 1899), pp. 71-119. (See pp. 93-95, and fig. 4.) 



