of Lake Superior. 33 



only. The more minute geological remarks on the north shore 

 will be rendered more clear by premising a few general state- 

 ments. 



A red-and-white sandstone, for the most part horizontal, pre- 

 dominates on the south shore, resting in places on granite. It 

 shews itself on the north shore near Pigeon Bay, is in great quan- 

 tity in the Maramelies and Nipigon Bay, and giving occasional 

 intimations of its existence at Cape Rlaurepas, and off Gravel 

 River, again floors the lake, from near Point Marmoaze to the Falls 

 of St. Mary; excepting at and about Gros Cap, which consists of 

 the clay porphyry of the Pay Plat, granite, and greenstone, 8fc. 

 Amygdaloid occupies a very large tract in the north, stretching 

 from Cape Verd to the Grand Portage (at least), profusely inter- 

 mingled with argillaceous and other porphyries, sienite, trappose 

 greenstone, sandstone, and conglomerates. Points Gargantua and 

 Marmoaze, with their neighbourhood, are of amygdaloid. It is 

 traced, in small quantity, to Gros Cap, by Major Delafield, and 

 constitutes moreover the gi-eat promontory of Keewawoonna, asso- 

 ciated with other forms of hornblende rocks. At Points Gar- 

 gantua and Marmoaze only could I detect a stratification in any 

 of these rocks, but the two last enumerated above. The amygda- 

 loid there runs N. and NNE.*, with a westerly dip. 



Trappose-greenstone is the prevailing rock from Thunder Moun- 

 tain westward, and gives rise to the pilastered precipices in the 

 vicinity of Fort William. It passes northward into the interior, 

 and ceases at the west end of Gun-flint Lake, in Ion. 90° 45', on the 

 old route to the Lake of the Woods, nearly opposite to the en- 

 trance of Two Island River into Lake Superior. Mr. Thompson 

 informs me tliat, mixed with sienite, this rock is continued west- 

 ward, nearly, if not quite, to the River St, Louis. The 

 portion of the northern and eastern shore not yet noticed, in- 



* The following are the results of all the observations by Mr. Thompson on 

 magnetic variation in Lake Superior, with which I am acquainted, but I hope 

 to be furnished with more soon, vis. ; — at the River St. Louis, 5°E. ; 31 miles 

 west of Grand Portage, 2°E.; Fort William, C°fi|E. ; Thunder Point, 1°K. 

 Point Marmoaze, 6°E.; about Nipigon Bay the compass is much disturbed. 



Vol. XVIIL D 



