CAPE COD GEOLOGY 



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are distinctly different from those in the western area. They have no sharp ridges 

 and cones such as are seen in stratified deposits; they show the more subdued 

 forms of till moraines. The surface material is a sandy till containing no clay 

 and in places no pebbles. At a few places the ridges have a central core of older 

 till upon which the later moraine was laid. The moraines on both sides of Lagoon 

 Pond occupy high ground and lie above the level of the outwash plain just south 

 of it; those farther east occupy much lower ground, and few of them are as 

 high as the adjacent plain. 



KETTLES 



Kettles are numerous in both the western and the northeastern areas, and 

 many of them are occupied by small ponds or swamps. Those in the till moraine 

 are relatively shallow and have gently sloping sides ; those in the stratified mo- 

 raine are deeper, and many of them have steeper sides. The kettles of both 

 types are merely low undrained areas between ridges built up of material laid 

 down by the ice. Most of them are not ice-block holes, but depressions due 

 to the arrangement of the surrounding morainal ridges. Most of the kettles 

 in the till moraine have more regular outlines than those in the stratified moraine. 



There are at least two kettle valleys on the island. One is on the west side 

 of Lagoon Pond and the other, which is larger and contains a series of ponds, 

 is the valley in which James Pond lies. This valley was probably formed by the 

 building up of a series of recessional moraines rather than by buried ice. The 

 chain of ponds, however, although it is not well shown on the topographic map, 

 suggests a kettle valley. 



OLDER VALLEYS 



Conspicuous elements of the physiography of the morainal areas of Marthas 

 Vineyard are the old valleys cut in the Manhasset deposits. Although these 

 valleys were cut in unconsolidated beds, most of their larger features were not 

 changed by the action of the Wisconsin ice sheet. They may be divided into two 

 groups: (1) the more maturely developed and larger, which run south westward, 

 and (2) the more youthful, which are shorter and run at right angles to those 



of the first set. 



The first valley of group 1 to be considered here heads between Prospect 

 Hill and Peaked Hill, in the western area, and runs northeastward nearly parallel 

 to the shore as far as North Tisbury village, where the stream now occupying 

 it turns abruptly south. The original valley probably extended farther northeast 

 but is now filled with outwash gravel. No single continuous stream occupies 



