FELSITIC PORPHYRIES OF THE PORCUPINES. 211 
and non-polarizing, while thickly studded through this are minute particles 
of quartz, a number of which polarize together, thus showing that they are 
parts of one crystal. The section thus has a peculiar mossy appearance in 
polarized light. This quartz is doubtless secondary, but the particles are 
larger and more nearly like those of the original quartz than usual. The 
few porphyritic quartzes and feldspars present the usual characters. Much 
black dust is present in blotches and lines, and is in part undoubtedly mag- 
netite. The dark purplish quartz-porphyry (2574) from See. 20, T. 51, R. 
42 W. (500 N., 1150 W.), holds a few minute original quartzes, and shows 
under the microscope a matrix which in the ordinary light appears nearly 
homogeneous and thickly dotted with minute brownish and blackish part- 
icles, but in the polarized light presents an appearance analogous to that of 
the last rock described, except that the secondary quartz is in much more 
minute particles, large numbers of which polarize together. Orthoclases 
occur among the porphyritic ingredients, and a very interesting relation was 
noted between one of the orthoclase crystals and one of the original quartzes, 
the latter having grown around the end of the former. A few minute augites 
occur in the matrix. A closely similar rock (2586) appears in large exposures 
on the upper part of the stream which enters the southeast end of Carp Lake, 
in the S. W. 4, Sec. 23, T. 51, R. 43 W. The sections of the dark purplish- 
red rock (1247 and 1248) from the bed of Little Carp River in the north- 
east corner-of Sec. 20, T. 50, R. 44 W., appear much like the last described, 
having not very rare original quartzes and orthoclases, and abundant second- 
ary quartz, some of which is arranged in curving concentric lines, appa- 
rently emphasizing a structure in the original rock. These sections show 
much fine ferrite, and now and then a quite perfectly developed augite crystal. 
The ferrite particles in places appear to indicate flowage. The ledge on the 
south line of Sec. 9, T. 50, R. 44 W., 270 paces west of the southeast corner, 
shows a very plainly banded felsitic porphyry (1259) with not rare, white 
orthoclase crystals which often lie entirely across two or three bands. The 
banding is produced by lighter and darker shades, and is quite irregular and 
wavy. Under the microscope the banding is seen to be produced by the 
presence of much red iron oxide in some bands, and its absence or relative 
scarcity in others. The bands are quite without regularity or continuity, 
