pe 
QUARTZLESS PORPHYRY. 93 
were found with a tendency to a vesicular structure, and then the thin sec- 
tion shows flowage lines and isotropic material at the maximum. 
The porphyritic feldspars are orthoclase and oligoclase, the latter the 
prevailing one. Both are always reddened and clouded by alteration. 
Many sections show also porphyritic augites, with crystalline outlines often 
remaining, and always with the peculiar red and brown, opaque, ferritic 
alteration-product, which characterizes the augites of all of the acid rocks 
here described. 
As instances of the occurrence of these porphyries—which are less com- 
mon than any of the other original rocks of the Keweenaw Series—may be 
mentioned the rock of the Stannard’s Rock reef; the prevailing pebbles of the 
Eagle River conglomerate, Keweenaw Point; the massive to vesicular rock 
of the old Suffolk mining location (Praysville), Keweenaw Point; many of 
the pebbles of the Portage Lake conglomerates ; the rock exposed in the bed 
of the Gogogashugun River in the northern part of Sec. 8, T. 46, R. 2 E., 
Wisconsin; the rock at the falls of the Brunschweiler River, NW. 4, See. 
22, T. 45, R. 4 W., Wisconsin; and a rock showing on the southwest shore 
of Michipicoten Island.1 
Called by T. Macfarlane ‘‘porphyritic melaphyr,” p. 138, Report of Progress of the Geological 
Survey of Canada for 1863 to 1866. 
