90 



BULLETIN or THE ESSEX INSTITUTE. 



est example of terminal moraine topography in the east- 

 ern United States, for the reason that the underlying pre- 

 glacial deposits have very little expression in the relief of 

 the area. On Martha's Vineyard and in the westward ex- 

 tension of the terminal moraine, an older topography at 

 almost every step accentuates the height and grandeur of 

 the morainal accumulations ; whereas, on Nantucket, the 

 approximate extent and bulk of the moraine and its posi- 



FiG. 3. A portion of the island of Nantucket, stiowing tiie frontal outwash 

 plain with Ice-contact slope (dotted belt between twenty and sixty feet contour- 

 lines), the fosse or depression at the head of the plain, and the kame moraine or 

 belt of mounds and kettles of submarginal drift. The contours represent some 

 of the larger creases on the plain. Contour interval, twenty feet. (From U. S. 

 Geological Survey, topography by E. B. Clark.) 



tion with reference to the ice may be clearly discerned. 

 (See Fig. 3.) 



From the existence of a terrace at the head of the sand- 

 plain which rises from forty to fifty feet above the depres- 

 sion or fosse on the north, it seems demonstrable that the 

 ice-front lay along the head of the plain while deposition 

 was taking place in the morainal tract proper. The knobs 

 and basins moulded in the unstratified drift, then, are 

 submarginal rather than precisely frontal in origin. In 



