236 CURTIS AND WOODWORTH 



lower stagnant prism of ice, the subglacial drainage is inter- 

 rupted and the detritus is involved in the movements of the 

 ice as in the case of the till. It is favorable to this view that, 

 in cases where such action may be invoked, eskers are absent, 

 and the sand plain appears to have been fed by streams flow- 

 ing off the ice sheet. 



Certain ponds and furrows which lie in the kame moraine 

 belt show that the drainage of the ice sheet, perhaps a late 

 phase of the system, coursed through the field quite independ- 

 ently of the motion of the ice, which may well have been stag- 

 nant at the time. On the east, the furrow connecting Polpis 

 harbor with the drainage crease in the sand plain has been noted 

 by Shaler, as an indication of the movement of subglacial water 

 as in a pipe to the front. On the other hand, creases west of 

 the town connecting with deep, pothole -like ponds in the 

 moraine belt suggest the holes at the bottom of falls of water 

 off the edge of the ice sheet rather than depressions due to the 

 melting out of blocks of ice. 



The question of sea level in relation to the sand plain at the 

 time it was building is a debatable one. The absence of any- 

 thing like wave action on the island above the present sea level 

 is presumptive evidence that the sea has not stood higher than 

 it now does upon this coast since the glacial formations were 

 deposited. A comparison of the Nantucket plains with the 

 deltas of glacial rivers such as those of the Malaspina district 

 in Alaska and of Heard Island in the Indian ocean would lead 

 us to regard the sand plain as made in the open air. 



The student who is desirous of studying many interesting 

 details concerning the geology and physical geography of this 

 island should supplement this brief account of some of its fea- 

 tures and the questions which they raise, by reading Professor 

 Shaler's report on its geology. 1 



J. B. Woodworth. 



x The Geology of Nantucket. Bulletin No. 53, 1889, U. S. Geol. Surv., pp. 55. 

 10 plates. By N. S. Shaler. This work gives references to numerous other papers 

 concerning the paleontology and moraines of the island. 



