SURFACE GEOLOGY. 15 
the great glacier moving from the north encountered here a high ridge, 
which, though altogether the result of erosion, seems to have had an 
anterior existence; since the ice rose up its northern side, planed all the 
slope, and curved round and embraced its irregularities as though it fol- 
lowed rather than fashioned the topography. In the excavation of the 
Lake Erie basin the glacier by which it was formed moved in the line 
of its major axis from Buffalo to the islands. In the immediate basin of 
the Lake the rocks are all planed, scratched, and sometimes deeply fur- 
rowed in this direction; while on the plateau between Lake Ontario 
and Lake Erie the bearing of the marks is nearly north and south. 
That the depths of the basin were not excavated by the glacier which 
produced these last named grooves is certain, from the fact that the east 
and west grooves prevail almost exclusively on the islands and on the 
immediate shore of the Lake; the north-south furrows being very rarely 
visible, and where the two systems are seen together, the east and west 
grooves seem to be the most recent. 
The central and eastern portions of the bed of Lake Erie were once 
occupied by quite soft rocks—Hamilton, Genesee, Portage and Chemung, 
and Waverly. Of these, more than a thousand feet in thickness were 
removed; and this portion of the basin was cut, to what depth we do not 
know, as it is much silted up, but certainly much deeper than elsewhere. 
When, however, the glacier which excavated the basin reached the Cin- 
cinnati arch it encountered a massive barrier of hard rock, which offered 
an obstinate resistance to its erosive action, and caused it to rise more 
than 300 feet above its eastern level. This barrier has been deeply. 
scored, and the islands of the Lake have been wrought out of the solid 
beds of the Corniferous and Helderberg limestones. As I have men- 
tioned elsewhere, previous to this time the basin of Lake Erie was tra- 
versed by a deep river channel, into which the profound gorges of Grand 
river, the Cuyahoga, etc., lead. Doubtless this river valley guided the 
excavation of the Lake Erie basin, as it did that of Lake Ontario. It 
traversed the area of the latter Lake nearly east and west, and connected 
with the Hudson through the Mohawk gap. 
After leaving the basin of the present Lake, the Erie glacier was 
deflected toward the south, and apparently flowed down the course of 
the Wabash. The following table gives the bearings of the furrows made 
by the Lake Erie glacier at different points: 
