228 CURTIS AND WOODWORTH 



practically dry, and represent the old drainage channels of 

 glacial time. Some of them can be traced, not only toward the 

 head of the sand plain, but extend quite through the kame 

 moraine to the harbor on the north. 



5. Po?ids or lakelets. — There are several types of ponds on 

 Nantucket. The most prominent lie in the lower ends of the 

 long narrow drainage channels across which the along shore 

 action has built barrier beaches. Hummock Pond, Long Pond, 

 Micomet Pond, etc., are the largest of these basins. Sachacha 

 and Gibbs Pond, by their circular forms alone would seem to be of 

 different origin. Gibbs Pond lies in a depression of the fosse, 

 Sachacha in a depression in the kame moraine across which a 

 barrier beach has been thrown. Croskaty Pond is simply the 

 unfilled enclosure between the trailing spits of Coatue Beach and 

 Great Point. On the inner side of Coatue Beach, lagoon-like 

 ponds have been formed behind the successive growths of sharp 

 cusps. "Three of the cusps on the inside of the Coatue Spit, have 

 no lagoons, but as the other two have, and since they are nearer 

 the end of the spit and hence probably later formed, it is quite 

 likely that the earlier formed forelands also began with lagoons." T 



Professor Shaler has ascribed these Coatue cusps to tidal 

 whirlpools. He says: "From a superficial inspection it appears 

 that the tidal waters are thrown into a series of whirlpools, which 

 excavate the shores between these salients and accumulate the 

 sand on the spits." 2 



6. Marshes and swamps are plentiful and of origin similar to 

 the ponds, the swamps as a rule being but the more advanced 

 stage of pond-filling. 



7. Shoreline topography is well exemplified. Nantucket's 

 south side shows a coast well straightened by the dominating 

 currents ; the irregularities have been smoothed by beaching 

 across the inlets and nipping the sand plain. A large part of 

 the eroded material has gone to build up both the long spit 

 extending toward Tuckernuck, and the rounded cusp or "apron" 



J F. P. Gulliver : Proc. Am. Acad. Arts and Sci., Vol. XXXIV, 1899, p. 219. 

 2 Bull. U. S. Geol. Surv., No. 53, 1889, p. 13. 



