104 Ei. Desor on the Drift of Lake Superior. 
small space in our diagram ; and as we advance towards the left, 
the drift terraces; and we shall have occasion hereafter to refet 
to such an origin for those differences of level which are to be 
+ I an uninterrupted manner over vast tracts of county; 
especially along the sea shore. But we should be careful to-cal 
in such causes only when the phenomena cannot be otherwis? 
explained. ; 
Ridges are often associated with terraces, and have frequently 
weden, where they go by the name of esars, (which | 
sand hills,) I shall designate them henceforth by that name 
There is every probability that they were formed as shoals; o 
