302 SURFACE GEOLOGY. 



these hills, is very irregular, consisting of hills, ridges, and rounds, with bowl-shaped 

 hollows which frequently contain ponds. This feature has led some to regard these 

 deposits as similar to kames.* Their material, however, is very different from that of 

 the kames, which consist principally of stratified water-worn gravel, rarely containing 

 any large or angular boulders, but frequently intermixed with layers of sand. 



The conclusion of Mr. Clarence King, that this island, which he examined, forms 

 part of a terminal moraine of the continental ice-sheet, seems to explain the accumula- 

 tion of the till in this remarkable series of hills. The border of the ice-sheet probably 

 remained almost stationary through a long period, in which the materials that it con- 

 tained were being continually brought forward and deposited at this line of its melting. 

 In many places these would be pushed into very irregular heaps and ridges by retreats 

 and advances of the ice-margin. At the same time we should also expect that thick 

 beds of ground-moraine would be gathered beneath the ice near its termination. The 

 withdrawal of the glacial sheet would then leave these deposits as upper and lower till, 

 one overlying the other, in a long but broken and undulating series of hills. 



This terminal moraine does not, however, mark the farthest limit reached by the 

 glacial sheet, which at one time extended six or seven miles beyond the Elizabeth 

 islands, as shown by the prominent range of drift hills, which forms the north-west 

 part of Martha's Vineyard. The origin of Cape Cod also seems to have depended upon 

 this greater extension of the ice-sheet. Its terminal front appears to have continued 

 from Martha's Vineyard north-easterly across Barnstable, thence to the east and north 

 along the inner shore of the cape to Truro, which it probably crossed, extending on- 

 ward to the north-east. This seems to be the outmost line at which we can assert the 

 former presence of the continental ice-sheet. 



Cape Cod, east from Sandwich, consists almost entirely of modified drift. Through 

 Barnstable this is disposed in kame-like ridges, knolls, and small plains, separated by 

 crooked and bowl-shaped depressions. The material here is gravel and sand, often 

 obliquely bedded, with frequent boulders which appear to have been dropped upon 

 these stratified deposits from floating ice. From Barnstable to South Wellfleet the 

 surface is mainly level, consisting of plains of fine gravel or sand, and boulders are 

 rarely seen. These plains vary in height from 25 to 75 feet above the sea. From 

 South Wellfleet to High Head in the north part of Truro, the contour on the west side 

 of the cape is again in very irregular kames, which are composed of gravel and sand 

 with only rare boulders. These deposits, like those in Barnstable, rise to a height 100 

 to 150 feet above the sea. The east side of the cape is here a nearly continuous bluff 

 of this height, horizontally stratified, being evidently a remnant of a nearly level plain, 

 the east part of which has been washed away by the sea. Thick beds of clay have 

 been exposed at a few points. At the Clay Pounds, near Highland light, the section 

 is sand at the top, about 40 feet ; finely laminated blue clay, also about 40 feet ; then 



* Proceedings of the Dostoyi Society 0/ Natural History , vol. xix, pp. 59-63; and American Naturalist, 

 vol. xi, pp. 674-680. 



