92 BULLETIN OF THE ESSEX INSTITUTE. 



Only in deep passes through the highlands, where the 

 ice-base was low, did the construction of the sand-plain 

 reach up to and above the base of the ice-sheet, hence the 

 plain usually comes up against the rising slopes of the 

 moniine without a definite terrace such as characterizes 

 the Nantucket plain. Evidences of ice-contact are shown 

 in the head of the James Pond depression (16) and again 

 in a high terrace south of the state road at Sachem Spring 

 in the region of Chappaquonsett Pond. There are fan-like 

 forms, between the state road and the eastern side of 

 Lagoon Pond and at an nveruf'e radial distance of two and 

 a half miles south of Vineyard Haven, which indicate the 

 extension of the ice-sheet up to the arc, thus described, at 

 a time just before the deposition of the Sachem Spring 

 terrace. 



The outer portion of this great plain is grooved by 

 sharply defined drainage creases, some of which are trace- 

 able up to the line of the moraine. Other creases appear to 

 have been originally thus extended but to have ])een later 

 choked up by the outpouring of gravels and sands along 

 the ice front. 



This plain, like that of Nantucket, has, at the present 

 time, an average slope of about twenty feet to the mile. 

 Its inner margin attains an elevation of one hundred feet 

 above the sea. It is relatively free from ice-block holes, 

 one such depression existing one and a half miles south 

 of the southern end of Lagoon Pond (15). Kettles are, 

 however, not wanting in the morainal or intraglacial field 

 of the time of deposition. 



Plains of the Cape Cod moraine. — A well recognized 

 line of moraine begins on Cape Cod, in Orleans (4), and 

 extends west-by-south next the shore of Cape Cod Bay, 

 curving northward to unite with the interlobate line of 

 moraine skirting the eastern shore (12) of Buzzard's Bay. 

 At the point of union (10), thick morainal deposits extend 



