GLACIAL DRIFT. 303 
sand, with occasional layers of gravel containing pebbles up to six inches in diameter, 
exposed for 20 feet, and probably extending as much farther to the sea-level. 
The accumulation of these thick deposits of modified drift, occupying an area more 
than forty miles long, with an average breadth of five miles, remote from any large 
river, and bordered on each side by the sea, seems capable of explanation only by sup- 
posing the material to have been held in an ice-sheet, which extended to the line that 
we have indicated, covering the Vineyard sound, Cape Cod and Massachusetts bays, 
and thence reaching to the north-east over a large part of the Gulf of Maine. When 
the return of a warmer climate drove back the front of these ice-fields to the long ter- 
minal moraine of the Elizabeth islands, Falmouth, Sandwich, and Plymouth, the rivers 
which flowed from their melting surface were principally discharged at two points, those 
at the south-west converging towards Barnstable, while those which descended from 
the glacial sheet over Massachusetts bay had their mouth in Wellfleet and Truro. The 
bordering walls and irregular masses and ridges of ice, which beset these rivers at their 
points of escape from the ice-sheet, caused their deposits over these areas to be massed 
in kames. The ocean at this period stood 150 feet or more above its present height; 
and the part of the burden of these glacial rivers, which was carried beyond their 
mouths, was spread by marine currents in nearly level plains, bordering the front of the 
ice-sheet. The true terminal moraine of till, formed by the ice at this bound of its 
greatest extent, is covered by the sea or by these beds of modified drift. 
The north end of these Champlain deposits is at High Head. The whole of Proy- 
incetown consists of sea-sand, with no pebbles. This sand has come from the erosion 
by the sea of the east shore of the cape; has been swept north and west to its present 
place in the lee of this breakwater ; lifted by the waves into beach-ridges ; and further 
raised by the wind into hills a hundred feet in height. 
On Long Island the farthest limit attained by the ice-sheet is probably indicated by 
a series of drift hills, which is commonly known as the «backbone of the island.” 
These hills are well exposed along the south shore for about ten miles west from Mon- 
tauk point, forming cliffs from 20 to 140 feet high. Westward, they extend through the 
north part of East Hampton, and from Sag Harbor south-west to the Shinnecock hills 
and Canoe place. Thence they continue in a nearly west course, including Osborn’s 
hill, a few miles south-west of Riverhead ; Terry’s hill, south of Manor ; Holman’s hill, 
north of Yaphank; the Coram, Seldon, and Bald hills; Mount Pleasant, west of Ron- 
konkoma lake; Pine hill; the Commac, Dix, and West hills; Spring, Wheatly, and 
Harbor hills, the last of which, near Roslyn, is the highest point on this island. Far- 
ther west, this series of hills trends a little more to the south, passing near Lakeville, 
and close north of Creedmoor, Jamaica, and East New York. Thence it nearly co- 
incides with the south-east boundary of Brooklyn, and reaches to the Narrows, forming 
the sites of Cypress Hill cemetery, Ridgewood reservoir, and the cemetery of the Ever- 
greens, of the highest portions of Prospect park and Greenwood cemetery, and of Fort 
Hamilton. 
The length of this range from Montauk point to the Narrows is about 115 miles. It 
