CAPE COD GEOLOGY 



63 



in its name. Great South Pond and Long and Halfway ponds and, farther south, 

 Great Herring Pond, have their longer axes in the line along which the group ex- 

 tends, about N. 42 W. Running out southwestward from each of the larger ponds 

 in this line, there are small depressions, the deeper parts of which are occupied 

 by ponds or drainage lines, such as that of Agawam River, draining Halfway 

 Pond. This complex group of sand hills, sloping plains, and ice block holes is the 

 most singular and at the same time the most regular in its repetition of features 

 due to the deposition of gravel and sand between and around blocks of ice that 

 lay in these depressions, the deeper of which contain bodies of standing water. 



The area of a certain group of these lakes appears to have been occupied by 

 the eastern margin of the Buzzard's Bay lobe of the ice sheet. From this margin 

 sloping plains of outwash were laid down by streams flowing southwestward, 

 toward Buzzard's Bay. These plains, which along their eastern margin rise to 

 elevations of 200 and 250 feet, have the appearance of large fans built between 

 ravines that have disappeared. 



That streams flowed from the ice front at this or a later stage across the 

 lower surfaces on the southwest is indicated by large drainage channels now 

 occupied by small streams, such as Agawam River. Great Herring Pond drains 

 into a channel that runs across the tract traversed by the Cape Cod Canal. The 

 central and western parts of this channel are occupied by Manomet River, 

 which has a course parallel to that of the smaller chains of lakes in the Plymouth 

 quadrangle and appears to be allied to them in origin, its bed having apparently 

 been occupied by a remnant of ice lying at the head of the Falmouth outwash fan. 

 In this respect the depression is analogous to the fosse on Nantucket, but it is 

 notably deeper and more complex in its relations to the neighboring glacial 

 features. This depression appears to have been followed by streams that flowed 

 from the Cape Cod Bay lobe or from marginal lakes in that lobate region west- 

 ward into Buzzard's Bay during the retreat of the ice from the Falmouth moraine. 



From the Nauset inlet northward to Pilgrim Heights, Cape Cod is com- 

 posed almost entirely of plains of stratified gravel, sand, and clay, though here 

 and there boulders are scattered on the highest surfaces in Truro or appear in 

 certain coastal areas in beds of gravel. These plains form three rather distinct 

 areas. The southernmost is the Eastham plain, already described as having been 

 built by water flowing westward from an ice mass lying outside the present area 

 of the Cape. It is the most perfect and most typical of the plains on the Cape 

 and is among the latest glacial features there, being probably somewhat more 

 recent than the fans and plains in the Plymouth interlobate district and on the 

 Cape farther southwest. 



