126 



CAPE COD GEOLOGY 



On the opposite part of the main island, in a stretch extending northwest- 

 ward nearly to the south end of Lagoon Pond, a distance of 6 miles, the ice contact 

 can be traced by means of boulders. In this stretch there is a gradual transition 

 from stratified moraine to out wash plain. 



The limit of the Cape Cod Bay lobe south of Lagoon Pond is marked by a 

 well-developed ice contact slope, which extends westward for about a mile and 

 then runs northwestward for about 2-| miles. The fosse here is not wide but is 

 well marked. North of the fosse, on the west side of Lagoon Pond, and on its 

 east side as far as the north end of Sengekontacket Pond, there are the largest 

 areas of stratified moraine on the island. The outwash plain is well developed 

 south of the ice contact slope. Beginning abruptly at the crest of the slope it 

 stretches away far to the south, declining in altitude at an average rate of 15 

 to 20 feet to the mile. In this area the head of the plain reaches its highest ele- 

 vation, approximately 100 feet, about a mile and a half west of the head of Lagoon 

 Pond. The plain here appears to owe its origin largely to the Cape Cod Bay lobe 

 and not to the Buzzards Bay lobe, for nearly all its drainage lines except those 

 in its eastern part point toward this lobe. The drainage lines in the eastern part 

 of the plain, especially on the west side of Edgartown Great Pond, run south- 

 eastward, but they are not long, and those farther west do not cross the main 

 creases, which run south westward. 



MORAINES 



STRATIFIED MORAINES 

 The moraines in the western area, which some geologists have called kame 

 moraines, are made of roughly stratified beds of sand and gravel that were de- 

 posited by water flowing from the melting ice. These moraines give this area 

 its characteristic aspect. Many of them are ridges whose long axes extend north- 

 eastward, but some are of irregular form. Such ridges are common in the 

 western area of Marthas Vineyard. 



TILL MORAINES 



On Marthas Vineyard till moraines are much less common than stratified 

 moraines, but at many places the two kinds can be distinguished only by ex- 

 amining their internal structure. The till laid down by the Wisconsin ice is sandy 

 and contains very little clay. The till moraine is rounder in form; it nowhere 

 presents sharp cones and ridges. Typical till moraines are common in the Gay 

 Head region. 



In the northeastern area the moraines formed by the Cape Cod Bay lobe 



