Geology of Lake Superior. 41 
7. We have now noticed all the genera of minerals 
which were met with on Lake Superior, and, in some instan- 
ces, the species also. We have not divided them into sub- 
species, for that would have been equivalent to a description. 
It will be seen that they are very numerous; their localities 
are, however, new and therefore valuable. 
- Simplicity seems to be characteristic of this lake, particu- 
larly in regard to its geology. The formations are few in 
number, but on a scale of grandeur not frequently met with. 
its geological features may be thussummed up- An irregu- 
larly oval basin is formed by the inferior order of rocks, hav- 
ing a broken belt or range of trap or overlying rocks on the 
inner declivity of its northera margin; and probably on its 
southern margin also, as these trap rocks were observed on 
the south coast, whenever the granite approached the lake. 
Lastly, an immense deposition of sandstone, formed from the 
ruin of parts of the foregoing rocks, extends from side to side, 
and end to end, of the lake; attaining the same elevation, 
and resting on granite on either side, containing the same 
component minerals and imbedded substances. ‘The granites 
of the north and south coasts are also similar. Both contain 
hornblende in large quantity, and are traversed by veins of the 
same nature. ‘These veins pass frequently from granite into 
greenstone, unaltered either in their nature or direction. 
This circumstance is one of the reasons which has induced us 
to class the last named rock ia the submedial order, instead 
of considering it asa trap or overlying rock. Its passage into 
sienitic granite, and its generally more crystalline na- 
ture, as compared with the basalt-like trap greenstone and 
veins, are others. We think we are correct in this classi- 
fication, but even if it should appear that we have made a 
distinction where none exists, it candono harm, It cannot 
mislead, for the facts are stated, and consequently any one 
may draw from them bis own couclusions, It is worthy of 
r remark 
