182 COPPER-BEARING ROCKS OF LAKE SUPERIOR. 
exceeded by only two or three elevations on the point, viz: Mount Bohe- 
mia, which rises to a height of 867 feet from the north shore of Lac La 
Belle; Gratiot bluff, and another point to the westward on the Bohemian 
Range, which exceeds 900 feet. Mount Houghton is rendered especially 
prominent by its isolation, the summit, which has a length of only about a 
hundred feet, being surrounded on the east and south sides by precipitous 
cliffs, while all around the ground falls off 200 feet within less than a quar- 
ter of a mile. 
The rock of which Mount Houghton is composed, and which shows 
in bold precipitous faces all about the top, is a light-pink to brick-red felsite, 
without visible porphyritic ingredients. The thin sections of this rock show 
also no porphyritic quartzes, but some orthoclases which might be called 
porphyritic. The sections vary from nearly colorless to a deep red, accord- 
ing to the amount of iron oxide present. The matrix in some sections 
appears to be wholly composed of feebly polarizing, minute orthoclases 
arranged in a felt-like mass, rarely with linear outlines to the crystals, and 
is nearly or quite destitute of any non-crystalline matter. Other sections 
show a much larger proportion of non-polarizing matter, and the feldspars are 
in thin tabular crystals, with sharply linear outlines. No quartz recogniza- 
ble as such could be detected with the microscope. Particles of black mag- 
netite are often included, though never abundant. No other accessory 
minerals were observed. Before the blowpipe this rock is fusible with 
difficulty, the lighter varieties being somewhat more difficult to fuse than 
the darker colored ones. The silica content is 76.9 per cent., or greater 
than it would be were there no silica besides that in the orthoclase. 
The general appearance of the mass of rock forming the summit of 
the mountain is such as to suggest a very high northern dip, some 75°, and 
this is further indicated by the abundant irregular parallel bandings in the 
rock of the top of the mountain. The appearance of lamination is pro- 
duced by waving bands of lighter and darker shading, which are often 
emphasized by minute quartz seams following their direction. 
To the eastward the same felsite shows in the Bare Hills, in Sec. 29, 
T. 58, R. 28 W., and beyond on the lake shore in section 28. Similar rocks 
appear on the east point of the bay into which the Little Montreal River 
i. 
