Geology of Lake Superior. i5 
There are other islands of the same kind, and near the same 
part of the lake. 
Of the trap rocks, sienite alone remains to be noticed, 
This is merely a greenstone with a superabundance of fel- 
spar. Its highly ferruginous nature, and its intimate con- 
nexion with the amygdaloids and porphyries into which it 
passes, together with the absence of chlorite, distinguish it in 
our opinion from the sienitic granite ; even although the last 
be destitute of both quartz and mica. Its felsparis never so 
ved as that of the sienitic granite ; but is often stained of a 
dark green colour by the hornblende, and iron rust brown, 
by the oxide of thatmetal which it almost always contains. It 
also strongly affects the compass needle, which the sienitic gra- 
nite never does. Lastly, it is always found in intimate associa- 
tion with the other trap rocks which we have enumerated, 
There were certainly appearances of stratification in the 
amygdaloid, but they were so very indistinct, and we could 
spare so little time to the examination, that we cannot ven- 
ture to assert this circumstance as fact. 
14. Medial order. The old red sandstone. This exten 
sive deposition forms the falls or rapids of St. Mary. It is 
again seen at the waters’ edge at Gros Cap: thence north- 
ward at Bachewine Bay, Ile Parisien, Sandy, Montreal, 
Lizard and Gravelly Islands, all of which are horizontally 
stratified, or nearly so. It may be traced, although in small 
quantities, almost to Michipicoten. Caribou island is formed 
of it. Between Michipicoten and the east point of Neepi- 
gon Bay it wasseen only as debris, but along the north side 
of the islands of that bay, and on itsnorthern and western 
shores, it appearsin high cliffs, and attains an elevation of 
about 400 feet above the lake. Continuing westward, it is 
found slong the islands of Black Bay. In the centre of 
that bay it forms several entire islands, We continue to trace 
it 
