1879. ] The Formation of Cape Cod. 559 
ruginous layer one to three inches thick. It rests, by abrupt 
change, upon gravelly sand containing pebbles up to one inch 
through, and within ten feet below they occur up to six or éight 
inches in diameter. The thickest portion of the clay is at the 
south edge of a gully some thirty rods north of the lighthouse, 
where the section is gravelly sand to forty feet above the sea ; 
clay fifty feet thick, and sand at top twenty-five feet. The upper 
part of the clay here and generally, is more sandy than its base, 
but it is still quite distinctly separated from the overlying sand. 
A quarter of a mile north the clay becomes narrower, and its 
base is higher, the section being sand and gravel to sixty-five feet 
above the sea, clay ten feet, and sand at top fifteen feet. Heights 
along this portion of the cape are as follows: in Eastham, fifty to 
seventy-five feet; Lombard’s Head, in Wellfleet, about one hun- 
dred and twenty-five; highest portion of bluff in south part of 
Truro, one mile south of Pamet river, about one hundred and 
fifty; Small’s hill, one mile north-east from Truro village, highest 
point beyond Barnstable on the cape, about one hundred and 
seventy-five ; bluff one mile south of Highland Light, one hun- 
dred and sixty; base and focal plane of this lighthouse, one 
hundred and thirty and one hundred and eighty-five ; High Head, 
about seventy-five. 
As in Plymouth county the accumulation of these thick and 
extensive beds of modified drift, remote from any large river and 
here bordered on each side by the sea, seems capable of explana- 
tion only by supposing the material to have been held in the ice- 
sheet and deposited by the floods produced at its retreat. When 
the return of a warmer climate drove back the front of these ice- 
fields from their terminal moraine upon Cape Cod, the rivers 
which flowed down from their melting surface were discharged 
upon these areas, those at the south-west converging upon Ply- 
mouth county, while those which descended from the glacial 
Sheet over the west part of the Gulf of Maine had their mouth 
in Wellfleet and Truro. 
The only fossils that have been found on Cape Cod occur in 
the bluffs on the east shore of Truro, as follows: One mile 
south from the head of Pamet river the section shows gray sandy 
clay at base to about thirty feet above the sea; ferruginous gravel, 
containing broken and worn shells, and with its largest pebbles 
-four inches through, five feet; overlain by more than one hun- 
