84 Tlie American Geologist. August, ib99 
yard, and Nantucket, extend from the front of the outer mo- 
raine belt several miles southward across the declining gravel 
and sand plains to the sea. Thirty of these remarkable valleys, 
now dry or in part occupied by small streams, were noted by 
Elias Lewis, Jr., within a distance of about sixty-five miles on 
the southern plains of Long Island; and he ascertained that 
they continue below the present sea level, being traceable be- 
neath the water of the inclosed bays to the beach ridge that 
divides them from the open ocean. Shaler ascribes such valleys 
on the New England islands to streams of fresh water issuing 
from beneath the ice-sheet and continuing in these clearly de- 
fined channels of their own erosion several miles onward under 
the heavy salt water of the sea. Instead I agree with Lewis 
that the valleys were subaerial courses of drainage from the ice- 
sheet, showing that the sea at this latitude, when the ice melted 
back from its farthest limit, did not reach so high upon the land 
as now. 
Tilting and Folding by the Ice-sheet. 
During the preglacial period of elevation, rivers flowing 
along the present beds of Vineyard sound and Buzzard's bay 
had eroded broad and deep valleys in the soft Tertiary and Cre- 
taceous formations, as the rivers of the same time flowing on 
the area of Long Island sound had doubtless also done. The 
ice-sheet then became amassed upon the higher lands at the 
north and in these valleys, filling and covering them, until even 
near its southern limit it was hundreds of feet thick. In its slow 
but mighty outflow the ice-sheet pressed across such trans- 
verse valleys against the ridges on their southern side with a 
force which I believe to have been the cause of the frequently 
disturbed condition of the incoherent sand and clay beds that 
there underlie the till and marginal moraines. Very excep- 
tional distortion and folding of these beds are recorded by Mer- 
rill, Hollick, Shaler. the present writer, and others, at many 
places on Staten island. Long island, Gardiner's island, the 
New England islands, and Cape Cod, coextensive with the in- 
vasion of the Cretaceous and Tertiary area by the ice-sheet. 
All these authors who endeavor to account for this dis- 
turbed belt, excepting Shaler, appeal to ice thrust; and I doubt 
that the grandest exhibition of tilting and folding of these beds 
in the very interesting and peculiar Tertiary section of Gay 
