374 Sketch of llennj Carvlll Lewis— Uph am. 
With the similar exploration of other portions of this great 
moraine done a few years earlier hy Prof. Chamberlin in Wis- 
consin, Profs. Cook and Smock in New Jersey, and the present 
writer in Long Island, thence eastward to Nantucket, and Cape 
Cod, and also in Minnesota, it completed the demonstration of 
the formation of the North American drift by the agency of 
land-ice. 
The observations of the moraine in Pennsylvania, detailed in 
this volume, are summarized by Prof. Lewis as follows: "The 
line separating the glaciated from the non-glaciated regions is de- 
fined by a remarkable accumulation of unstratified drift material 
and boulders, which, heaped up into irregular hills and hollows 
over a strip of ground nearly a mile in Avidth, forms a continu- 
ous line of drift hills (more or less marked) extending com- 
pletely across the state. These hills vary in hight from a few 
feet up to 100 or 200 feet; and while in some places they are 
marked merely by an unusual collection of large transported 
boulders, at other places an immense accumulation forms a 
noteworthy feature of the landscape. When typically developed 
this accumulation is characterized by peculiar contours of its 
own — a series of hummocks, or low conical hills, alternate short 
straight ridges, and inclosed shallow basin-shaped depressions, 
which like inverted hummocks in shape are known as kettle holis. 
Large boulders are scattered over the surface; and the unstratified 
HH which composes the deposit is filled with glacier-scratched 
boulders and fragtnents of all sizes and shapes." 
From its lowest point in Pennsylvania, where it crosses the 
Delaware, 250 feet above the sea level, this terminal moraine ex- 
tends indiscriminately across hills, mountains and valleys, rising 
over 2,000 feet above the sea in crossing the Alleghenies and 
attaining the maximum of 2,580 feet on the high table-land 
farther west, being there "finel}^ shown at an elevation higher 
than anywhere else in the United States." 
Preliminar}'^ outlines of professor Lewis' work on the glacial 
drift of England, Wales and Ireland are given by his papers in 
the reports of the British Association for 1886 and 1887, and 
the first of these also appeared in the American Naturalist for 
November, and the American Journal of Science for December, 
1886. Their most important new contribution to knowledge 
consists in the recognition of the terminal moraines formed by 
