102 E. Desor on the Drift of Lake Superior. 
beew observed in this region, which will be noticed hereafter. — 
Groovings of all sizes occur. The most common form is: 
of parallel furrows from one to two and four lines wide—some 
times extending but a foot, at others many yards. Where the 
rock is excessively hard they are mere striz, which are often 3 
distinct and sharp as though they had been graven with the point 
of a diamond. ollow spots are observed, as though they had 
been scooped out by a round instrument; also, we observe wide 
bowl and trough-shaped depressions, which have been caused by 
the same agency, since they are always found parallel with the 
strie. Instances of all these different forms exist on both 
of the lake and on Isle Royale. 
. As to the direction of the strie in this district, it will be seet 
that, with the exception of a few local deviations, it is north 
east and southwest—a direction which also prevails along the 
western shore of Michigan, and in portions of the western States 
This direction forms a striking contrast with that which pre 
throughout New England. There, they bear northwest and 
southeast. We shall hereafter attempt to explain this singulat 
opposition in the strie of the two regions east and west of the 
leghanies, and show their relation to the leading features of 
the continent. 
6. Terraces and Ridges.—The terraces and ridges of the great 
lakes have of late attracted a good deal of attention, inasmuch 
as they have a direct bearing upon the question of the changes 
of level which the surface is supposed to have undergone during 
the epoch of the drift. They may be seen both on the south 
and the north: shores of Lake Superior, though they are less 
striking here than around the lower lakes, (Erie and Ontario.) 
Those of thenorth shore of Lake Superior have been descr ibed 
by Mr. Logan. They are most conspicuous at a locality called 
“ Les Petits Ecrits,” of which Mr. Bliott Cabot has given a fine 
sketch in his Narrative. Those of the south shore have thus fat 
been but little noticed, probably because they occur chiefly 
in that portion of the lake-distriet which is least visited, vid! 
between the Saut and Keweenaw Point. 2yond that 
there may be seen, in many places, along the shore of the coppe 
region, high bluffs of drift; but they nowhere assume that staif 
ike form which is the characteristic feature of terraces.* . 
ba ead pbs and class as we ah Ehave to allude tracgucatly er 
materials which terminate abruptly in steep alopea We sles ot the sloped 
