NANTUCKET, A MORAINAL ISLAND 227 



tion across the island (Fig. 2) may be briefly described under 

 the following divisions. 



1. The ground ?noraine : an area of irregularly distrib- S 

 uted detritus, the undifferentiated till which lies on the 

 northeast part of the island in the vicinity of Pocomo 

 Head. (See map, Plate I.) 



2. The kame moraine: a belt or ridge of kame-like 

 mounds and kettles from 20 to 100 feet in altitude, 

 which, running through the middle of the island, seems 

 to form its back bone. On its south side, the kame 

 moraine, descending to the 40-foot level, grades sud- 

 denly into a smooth -bottomed trough, which reaches 3 

 the breadth of over one half a mile in its widest part. ' M 

 The southern side of this depression ascends 40 feet by I 

 an abrupt slope into the head of the sand plain. This g, 

 ditch-like conformation lying' between the kame moraine n 

 on the north and the sand plain on the south, runs 8 

 throughout the extent of Nantucket, and Tuckernuck, § 

 and has been termed : q 



o 



3. The fosse. — It is supposed that this depression » 

 marks the resting place of the ice, while the steep slope p 

 rising to the head of the sand plain marks the position g 

 of the ice front during the building of the frontal plain, 2- 

 This escarpment at the head of the sand plain has been a 

 called the ice-co?itact slope. a. 



4. The glacial sand plain: which, falling gently from 

 the terrace at its head to the sea on the south, represents 

 the sand and gravel deposited from the streams as they 

 flowed from the glacier front. The plain has a relatively 

 smooth surface, sloping in its two miles of extent, from 

 the 60-foot level to the cliff where the sea has cut the 

 20-foot level. At rather regular intervals of a quar- 

 ter of a mile, the plain is interrupted by shallow troughs. 

 These grade very gently into the head of the sand plain, 

 and continue southward until truncated in their deepest 

 expression by the seashore. These creases are today 



