CAPE COD GEOLOGY 



205 



The island is now treeless, but it was forested when Europeans first visited 

 it. Its surface is strewn with glacial boulders, and the hollows contain small 

 swamps and beds of peat. In 1915-16 a single farmhouse stood back of the 

 sandspit, and a few fishing stages or temporary huts on the cliff were being 

 taken down. The present proprietor of the island has constructed, on the west 

 side of the sandspit, a breakwater suitable for the protection of a small yacht. 

 During recent years the island appears to have been used chiefly for grazing sheep. 



DESCRIPTIVE GEOLOGY 



Earlier Investigations 



Owing to the inaccessibility of the island it has seldom been visited by 

 geologists. It appears not to have been examined during the first State survey, 

 made under Edward Hitchcock. It was referred to by Wright 1 as the "extreme 

 terminal moraine," but it was first described by Shaler in his report on the 

 geology of Marthas Vineyard, published in 1888, 2 which contained a geological 

 map of the surficial Pleistocene deposits. 



Shaler found that the island consists wholly of glacial drift. He recognized 

 a lower till or boulder bed, which was overlain by beds of blue clay. Above a 

 series of beds of fine sand and gravel he found another bed of till, which was 

 capped in turn by deposits of gravel that he compared with kames. Much of 

 this surface material, as he noted, "seems to have been shoved about in the 

 forward movement of the ice in front of which it was formed." 



The authors visited the island on September 11, 1915, and again on June 

 14, 1916, in company with W. C. Alden, of the U. S. Geological Survey. 



A walk eastward around the beach of the island from the landing place on 

 its north side affords an excellent view of the complicated structure of the 

 folded beds in the cliffs and shows that the form of the surface is independent 

 of the stratigraphy of the island. This surface truncates formation after formation 

 from point to point about the island. It shows striking morainal relief in its 

 hollows and hillocks, but these, like those of the central submarginal moraine 

 on Nantucket, are the effects of the corrugation of an older surface of erosion, 

 which cuts across the underlying Pleistocene deposits. 



1 Wright, G. F., The Ice Age in North America, p. 123, New York, 1891. (Contains reference to 

 earlier publications.) 



2 Shaler, N. W., Report on the geology of Marthas Vineyard, Seventh Ann. Rept., U. S. Geol. Survey, 

 pp. 352-353, fig. 63, 1888. 



