"133 
THE GEOLOGIST. 
and furrowed as beneatli the drift in Northern Europe. The 
author next describes the ridges of sand and gravel surrounding 
the great lakes, and regarded by many as raised beaches. Those 
examined preserved a general parellellism to each other and to 
the neighbouring coast, and some of them have been traced for 
more than 100 miles continuously ; they vary in height, and are 
often very narrow at their summit, and from 50 to 200 yards 
broad at their base. Cross stratification is very commonly visi- 
ble in the sand ; they usually rest on clay of the boulder forma- 
tion, and blocks of granite, and other rocks from the north are 
occasionally lodged upon them ; they are steeper on the side to- 
wards the lakes, and they usually have swamps and ponds on 
their inland side ; they are higher, for the most part, and of 
larger dimensions, than modern beaches. Mr. Lyell compares 
them all to the osars in Sweden, and conceives that, like them, 
they are not simply beaches which have been thrown up b}^ the 
waves above water, but that many of them have had their fomi- 
dation in banks or bars of sand ; they are supposed to have been 
formed and upraised in succession, and to have become beaches 
as they emerged, and sometimes cliffs undermined by the waves. 
The transverse and oblique ramifications of some ridges are re- 
ferred to the meeting of chfi"erent currents, and do not resemble 
simple beaches. The author concludes that most of the ridges 
were formed beneath the sea or on the margin of marine sounds. 
Some of the less elevated ridges, however, may be of lacustrine 
origin, and due to the oscillations in the level of the land since 
the great lakes existed ; for unequal movements, analogous to 
those observed in Scandinavia, may have uplifted fresh-water 
strata above the barriers which divide Lake IMichigan from the 
basin of the Mississippi, or Lake Erie from Ontario, or the 
waters of Ontario from the ocean. Considerable differences of 
level may have been produced in the ancient beds of those vast 
bodies of fresh-water, while the modern deposit and the subja- 
cent Sihirian strata may, to the eye, appear perfectly horizontal. 
