SURFACE GEOLOGY. 27 



Gulf by the valley of the Mississippi. The difficulties in the way of 

 this theory are sueh, 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. Prom 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 Erie, 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 Erie 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 

 Drift 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 traced them down continuously 2,500 feet below the present snow line. Who- 

 ever goes there doubting the erosive power of glaciers, 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. 



