FELSITE AND QUARTZ-PORPHYRY. 103 
51, R. 43 W., and again in Sec. 31, T.50, R. 44 W.; the Minnesota coast 
in the S. W. 4, Sec. 28, T. 56, R. 7 W.; the same coast immediately below 
Grand Marais; the bed of the Devil’s Track River, Minnesota, for several miles 
from its mouth; and the islands off the harbor on the south shore of Michi- 
picoten Island; (2) for the kinds carrying porphyritic orthoclase, but no 
quartz—the central area of the Porcupine Mountains, where much of the 
rock is of this character; the N. W. 4 of Sec. 12, T. 37, R. 16 W., in the 
Clam Falls region, Polk County, Wisconsin; and the Minnesota coast, 
ten miles above the mouth of Split Rock River; (3) for the quartziferous 
kinds—the line of the Torch Lake Railroad, Keweenaw Point, Sec. 36, T. 
56, R. 33 W.; the hill known as the “North Brother,” near Rockland, Mich., 
N. E. 4, See. 9, T. 50, R. 39 W.; the bold bluffs in the northern part of T. 
49, R. 42 W., Mich.; the central area of the Porcupines, where, however, 
the prevailing rock is without porphyritic quartz; the bed of Potato River, 
S. E. 4, Sec. 15, T. 46, R. 1 W., Wisconsin; the mouth of Tyler’s Fork of 
Bad River, S. E. 4, Sec. 17, T. 45, R. 2 W., Wisconsin; the islands off the 
north point of Beaver Bay, on the Minnesota coast; the Great Palisades, 
Baptism River point, and Red Rock Bay, all on the same coast; Bead Island 
at the mouth of Nipigon Straits on the Canadian coast; and the east 
shore of Michipicoten Island. 
The detailed descriptions of the following tabulation cover a sufficient 
number of occurrences to substantiate the general descriptions above given. 
Other thin sections of these rocks are briefly described in connection with 
the detailed descriptions of Chapters VI and VII 
‘Mr. M. E. Wadsworth, who has described (op. cit., pp. 113-120) a number of these sections of peb- 
bles of felsite and of the granite-like rocks which I describe below under the name of augite-syenite, 
was the first to note the occurrence of secondary quartz, and of an apparently spherulitic structure in 
these rocks, 
