. a 
4 . UF atic Phenomena about Lake Superior. | 89. 
s* 
glaciers yet in existence. Never do we find that water leaves 
the boulders which it carries along in regular walls of mixed ma- 
te terials; nor do currents any where produce upon the hard rocks 
tn situ the peculiar grooves and scratches which we see every- 
Where 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 fur-.% 
rows are sinuous, acting more powerfully upon the soft parts of 
the rocks or fissures already existing ; whilst glaciers smooth and 
~. level uniformly, the hardest parts equally with the softest, and, 
like a hard file, rub to uniform continuous surfaces the rocks upon 
which they move. ; 
i But now let us return to our special subject, the erratics of ©. 
' North America. ' 
The phenomena of drift are more complicated about Lake Su- 
perior than I have seen them any where else; for, besides the 
general phenomena which occur everywhere, there are some pe- 
culiarities noticed which are to be. ascribed to the lake as such, => 
Which we do not find in places where no large sheet of wa- =~ 
gent geologists, to perceive the facts as they are, whenever they 
bear upon the question of drift, I cannot but repeat, what I have 
already mentioned more than once, but what I have observed 
again here over a tract of some fifteen hundred miles, that the 
rocks are everywhere smoothed, rounded, grooved and furrowed 
ma uniform direction. The heterogeneous materials of which 
the rocks consist are cut to one continuous uniform level, show- 
ing plainly that no difference in the polish and abrasion can be 
attributed to the greater or less resistance on the part of the rocks, 
but that a continuous rasp cut down every thing, adapting itself, 
however, to the general undulations of the country, but never- 
theless showing, in this close adaptation, a most remarkable con- 
tinnity in its action. 
That the power which produced these phenomena moved in 
the main from north to south, is distinctly shown by the form of 
the hills, which present abrupt slopes, rough and sharp corners 
towards the south, while they are all smoothed off towards the 
north 
Indeed, here, as in Norway and Sweden, there is on all the 
hills a lee-side and a strike-side. As has been observed in Nor- 
way and Sweden, the polishing is very perfect in many places, 
times strictly as brilliant as a polished metallic surface, and 
Series, Vol. X, No. 28.—July, 1850. 
