SURFACE GEOLOGY. 199 
On the peninsula between Lake Erie and Lake Huron the 
Erie clays fill the old channel which formerly connected 
these lakes, having a thickness of over two hundred feet, 
and containing a few scattered stones. 
4th. Above the Erie clays are sands of variable thickness 
and less widely spread than the underlying clays. These 
sands contain beds of gravel, and, near the surface, teeth of 
elephant have been found, water-worn and rounded. 
5th. Upon the stratified clays, sands, and gravel of the 
Drift deposits are scattered boulders and blocks of all sizes, 
of granite, greenstone (diorite and dolerite), silicious and 
mica slates, and various other metamorphic and eruptive 
rocks, generally traceable to some locality in the Eozoic 
area north of the Jakes. Among these boulders many 
balls of native copper have been found, which could have 
come from nowhere else than the copper district of Lake 
Superior. 
Most of these masses are rounded by attrition, but the 
large blocks of Corniferous limestone which are scattered 
over the southern margin of the lake basin in Ohio show 
little marks of wear. These masses, which are often ten to 
twenty feet in diameter, have been transported from one 
hundred to two hundred miles south-eastward from their 
places of origin, and deposited sometimes three hundred feet 
above the position they once occupied. 
6th. Above all these Drift deposits, and more recent than 
any of them, are the “lake ridges," — embankments of sand, 
gravel, sticks, leaves, etc., which run imperfectly parallel 
with the present outlines of the lake margins, where high- 
lands lie in the rear of such margins. Of these, the lowest 
on the South shore of Lake Erie is a little less than one 
hundred feet above the present lake level; the highest, some 
two hundred and fifty feet. In New York, Canada, Michi- 
gan, and on Lake Superior, a similar series of ridges has 
been discovered, and they have everywhere been accepted as 
evidence that the waters of the lakes once reached the points 
