250 THE CANADIAN NATURALIST. [Jan. 



It also contains light red and ash-grey crystalline grains of 

 felspar, and others which appear earthy and decomposed. 

 The matrix is fusible, in fine splinters only, to a white enamel. 

 The rock has an uneven fracture, a specific gravity of 2.493, and 

 is probably a porphyritic quartz-trachyte. The other rock, which 

 occupies a very considerable area, partakes more of the character 

 of felsitic porphyry, although the felspar crystals are very often 

 indistinct. It contains, besides these, numerous grains of greyish 

 quartz, sometimes one-eighth of an inch in diameter, and a fine- 

 grained, dark red, difficultly fusible, matrix. The specific gravities 

 of three different specimens were found to be 2.54-8, 2.579, and 

 2.583. The bedding of the rock, if it possesses any, is very 

 obscure ; but it shews in places a tendency to separate into flags. 

 It has a very rough uneven fracture, and is probably also 

 quartzose trachyte. At the north-east corner of the Island it 

 seems to overlie, unconformably, beds of trap, which here assume 

 something like the ordinary strike and dip, viz., N. 72° E., dip 

 25° S. E. 



The islands which lie opposite the mouth of the harbour on the 

 south shore are composed of a peculiar rock, which is nowhere 

 visible on the main island. It consists of a reddish-brown im- 

 palpable matrix, with a hardness but slightly inferior to that of 

 orthoclase, in which minute spots of a soft yellowish-white material 

 are discernible. There are also lighter flesh-coloured grains ob- 

 servable, which seem to be incipient felspar crystals. The matrix 

 is difficultly fusible to a colourless blebby glass, and the specific 

 gravity of the whole rock, where freshly broken, is 2.469. A 

 piece slightly bleached to a greyish-white, from its adjoining 

 a crack in the rock, gave a specific gravity of 2.477. Some parts 

 of it exhibit a slightly porous structure, but this was not the case 

 with either of the pieces whose specific gravity were determined. 

 The rock has a very uneven fracture, and is probably trachytic 

 phonolite. The occurrence of these trachytic rocks on Michipi- 

 coten Island is very interesting, for they are the only ones of the 

 region which have in other countries been found in connection 

 with undoubted volcanoes. 



The general strike of the strata of the rocks of Point 

 Keweenaw, at least in the neighbourhood of Portage Lake is N. 

 30° to 40° E., and the dip 55° to 70° north-westward. The 

 melaphyres predominate, although polygenous and porphyritic 

 conglomerates are also frequent. The copper-bearing tufaceous 



