SURFACE GEOLOGY. Dia 
Gulf by the valley of the Mississippi. The difficulties in the way of 
this theory are such, however, that I am sure Prof. Dawson, clear-sighted 
and conscientious as he is, would abandon it if he could examine with 
his own eyes the surface geology of the lake-basin and the Mississippi 
valley. Without going into a lengthy argument to disprove this view, 
I will mention one or two facts which seem to me incompatible with it. 
First. The basins of Lake Erie and Lake Ontario have unquestion- 
ably been excavated by glaciers, and not by icebergs. The evidence of 
this is conclusive. From my own observations on the erosive action of 
glaciers in the Alps and in the Rocky Mountains and the Sierra Nevada, 
I do not hesitate to assert that the inscription left on the bottom and 
sides of Lake Erie was made by a glacier, and nothing else. The uni- 
form, continuous, and exact furrowing of horizontal and vertical sur- 
faces which is visible among the islands of Lake Hrie, is the precise 
counterpart of that which is executed by glaciers, and it certainly could 
not have been done by floating ice.* 
Second. A deep, broad ocean current flowing through the lake-basin 
from the Gulf of St. Lawrence would certainly have brought marine 
shells further than they have been traced by Prof. Dawson, and we 
should now find them more or less abundantly throughout our Hrie clay. 
Third. We should find in our Drift deposits abundant representatives 
of the rocks which form the shore of eastern Canada, Labrador, etc., but, 
so far as I know, not a trace of any of these rocks has been discovered 
in our Drift; while, on the contrary, nearly all the constituents of the 
Driit can be traced to places of origin in localities north and north-west 
of Ohio. Some of these materials are so peculiar, such as the native 
copper, and epidotic rock containing metallic copper, and this copper 
including specks of silver, that there can be no possible mistake about 
its derivation. The discovery of northern Drift in Louisiana has been 
suggested as an argument in favor of this hypothesis, but it should be 
remembered that this drift lies at the bottom of the entire Quaternary 
* Probably no finer exhibition of glacial markings exists in the world than those 
which cover the summits and slopes of the Cascade Mountains in Oregon. Here we 
find, over hundreds of square miles, rocks of all kinds, planed, polished, and 
grooved in the most surprising way. These markings lead from various centers, and 
I have traccd them down continuously 2,500 feet below the present snow line. Who- 
ever goes there doubting the erosive power of elaciers, will come away doubting no 
longer. And whoever comes from this scene of stupendous Alpine glaciation to the 
glaciated rocks of Ohio, and especially of the islands in Lake Erie, will not hesitate 
for a moment to attribute the inscriptions he finds here to the same agent that has 
planed and scored the slopes of the Oregon mountains. 
