100 FE. Desor on the Drift of Lake Superior. 
transportation is further confirmed by the boulders of the beach 
itself, which point likewise to the north as their birth-place. 
This applies especially to the copper region west of Keweenaw 
Point. There trap and sandstone are the only rocks in place; 
and yet among the boulders scattered over the surface there are 
many of granite and hornblende, which have evidently their 
origin on the opposite shore, where we know these rocks to be 
very abundant. ‘Thus it happens that, when travelling from 
south to north, the appearance of a new formation is always il 
dicated by the oceurrence of single boulders of it, whilst nothing 
of the kind takes place when travelling from north to south 
This precession of the boulders is especially striking among the 
ridges of the iron region north of Carp river, where there is often 
a great variety of structure in the rocks of the different ridges 
There the valleys between the different ridges contain, for the 
most part, boulders from the next ridge to the north. There ale 
also instances where a ridge did not allow the fragments of the 
preceding ridges to pass. A striking instance of this has beet 
observed by Mr. Hill west of Jackson location, where the slate 
and iron boulders are heaped up in great quantities on the north 
ern slope of a greenstone dyke, whilst there are none on the 
granite slopes south of this dyke, which has therefore acted as # 
barrier, preventing their transportation farther south. ‘This [tr 
itation prevails, however, only within the hilly portion of the 
e Superior region, between the lake shore and the dividing 
ridge. South of the ridge nothing of the kind seems to occu 
There being no further barrier to check their course towards the 
south, they have travelled even to the very limit of the drift de- 
posit; and thus it happens that boulders of the Lake Superiet 
region are found as far south as the Ohio—that is to say, mol 
than six hundred miles from the dividing ridge, the nearest place 
from which they could possibly be derived. We think, there 
fore, that there is satisfactory reason to consider the region of 
ke Superior, and especially the rim of cliffs and hills W 
surrounds its basin, as the birth place of the greatest quantity of 
This, of course, is in itself a proof that they have been deposited 
posteriorly to these formations. But becatise they are of a more 
