THE ERRATIC PHENOMENA. 401 



a sheet of ice sufficiently large to carry the northern erratics into their 

 present limits of distribution ; but this difficulty is greatly removed 

 when we can trace, as in the Alps, the progress of the boulders 

 under the same aspect from the glaciers now existing, down into 

 regions where they no longer exist, but where the boulders and other 

 phenomena attending their transportation show distinctly that they 

 once existed. 



Without extending further this argumentation, I would call the 

 attention of the unprejudiced observer to the fact, that those who 

 advocate currents as the cause of the transportation of erratics, have, 

 up to this day, failed to show, in a single instance, that currents can 

 produce all the different phenomena connected with the transporta- 

 tion of the boulders which are observed everywhere in the Alps, and 

 which are still daily produced there by the small glaciers yet in 

 existence. Never do we find that water leaves the boulders which it 

 carries along in regular walls of mixed materials ; nor do currents 

 anywhere produce upon the hard rocks in situ the peculiar grooves 

 and scratches which we see everywhere under the glacier and within 

 the limits of their ordinary oscillations. 



Water may polish the rocks, but it nowhere leaves straight 

 scratches upon their surface ; it may furrow them, but these furrows 

 are sinuous, acting more powerfully upon the soft parts of the rocks 

 or fissures already existing ; whilst glaciers smooth and level uni- 

 formly, the hardest parts equally with the softest, and, like a hard 

 file, rub to uniform continuous surfaces the rocks upon which they 

 move. 



But now let us return to our special subject, the erratics of North 

 America. 



The phenomena of drift are more complicated about Lake Supe- 

 rior than I have seen them anywhere else ; for, besides the general 

 phenomena which occur everywhere, there are some peculiarities 

 noticed which are to be ascribed to the lake as such, and which we 

 do not find in places where no large sheet of water has been brought 

 into contact with the erratic phenomena. In the first place, we 

 notice about Lake Superior an extensive tract of polished, grooved 

 and scratched rocks, which present here the same uniform character 

 which they have everywhere. As there is so little disposition, among 



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