PORPHYRY AREA OF THE PORCUPINES. ata 
Carp River, in the northeast corner of Sec. 20, T. 50, R. 44 W., the contact 
of the porphyry with the overlying rock is in sight. The high ridge of 
porphyry in the east part of section 31 and the southeast of section 30 of the 
same township proves that the boundary of the overlying belt of diabase 
and diabase-amygdaloid makes here a considerable deflection to the west- 
ward from a straight line drawn between its positions on the Little Carp 
River in See. 20, T. 50, R. 44 W., and in the west part of Sec. 18, T. 49, 
R. 44 W. Sec. 32,7. 51, R. 44 W., exposes porphyry largely in the south- 
eastern and southern portions, and diabase in the western and northern, 
while in the stream at the northeast corner of this section, lilac felsite and 
amygdaloids are largely exposed at only 200 paces from each other. South 
of Carp Lake, in sections 23 and 22, the porphyry and overlying rock are 
largely exposed at points not far apart, and several exposures of the two 
rocks between here and the junction in the N. EK. 4, Sec. 32, serve to fix 
this part of the boundary quite closely. The road running east and south 
from the head of Carp Lake, through sections 23 and 24, crosses ledges 
both of the porphyry and its overlying rock. In Sec. 30, T.51, R. 42 W., the 
limit is again found in the northeast quarter of the section. Further south- 
east, in T. 51, R. 42 W., there is some doubt as to the exact limit of the 
porphyry to the eastward, or rather, the position of its overlying rock is 
left in doubt by lack of exposures; besides which some doubt is introduced 
by the uncertainty as to where the fault lying south of the porphyry ends. 
Closely approximated exposures of the porphyry and amygdaloid on 
the south fix the southern limit very closely in sections 3, 4, 5, and 6, 
T. 50, R. 43 W. In the eastern part of T. 50, R. 44 W., a gap without 
exposures leaves the exact position of the eastern limit in some doubt, 
as indicated on the map. The porphyry and felsite ledges are so generally 
distributed over the area colored for those rocks as to indicate that they 
underlie most of its extent, but in one place a large exposure of a rather 
coarse-grained very highly crystalline gabbro, such as is frequently asso- 
ciated with porphyry and felsite on the north shore of Lake Superior, was 
noted. This is on the south line of Sec. 3, T. 50, R. 44 W., 1,150 paces west 
of the southeast corner. The ledge is 100 feet high and 200 feet long in a 
southwest direction. 
