OUTER TRAP BELT OF THE PORCUPINES. 219 
the second belt of basic rocks, with a thickness of some 300 to 400 feet. 
The rocks of this belt are finely exposed in the great cliff which stretches 
in a curving direction entirely across T. 51, R. 43 W., on the north side of 
the Carp Lake Valley. As already explained, to the eastward these rocks 
are found just capping the cliff, and then extending toa relatively long dis- 
tance down the north slope of the mountain; as, for instance, in Sec. 13, T. 
51, R. 42 W., where this belt has a surface width of over half a mile. 
Further west the junction with the underlying sandstone is lower down in the 
face of the great cliff, the belt descending but a short distance down the 
north slope of the mountain, and as a consequence presenting but a narrow 
spread on the map. Beyond T. 51, R. 43 W., to the westward, this belt 
pursues a course at first southwest and then more nearly south through T. 
51, R. 44 W.; T. 50, R. 44 W.; T. 50, R. 45 W., and T. 49, R. 45 W., to the 
Presqu’ Isle River, where there isa sharp bend to the westward, as indicated 
on the map. The best exposures are on the Little Carp, in Sec. 18, T. 50, 
R. 44 W., and on the Presqw’ Isle, in sections 14 and 15, T. 49, R.45 W. On 
both streams the junction with the overlying sandstone is exposed, and both 
streams make falls over the basaltic rocks, those on the Presqw’ Isle reaching 
a height of twenty-five feet. 
Eastward from T. 51, R. 43 W., this belt continues on an easterly 
course for some three miles, and then, turning, pursues a tortuous southerly 
course to the south side of T. 51, R. 42 W., whence, turning again ab- 
ruptly, it runs westward through the northern sections of T. 50, R. 43 W. 
Here it is found to come directly in contact with the central porphyry of 
the Porcupine Mountains, some 2,500 feet of rock that appears on the north 
side of the mountains being now absent, at least at the surface. This 
peculiar behavior I regard as the result of a fault, as indicated on the sec- 
tions of Plates XX and XXI. The peculiar serpentine course of the belt 
through T. 51, R. 42 W. is not conjectural, having been very satisfacto- 
rily made out from the locations and inclinations of a number of expo- 
sures. Moreover, it corresponds entirely with the courses marked out for 
the overlying belts. In the vicinity of the Unien mine, on sections 27 and 
22 of T. 51, R. 42 W., both upper and lower limits of the belt are well 
exposed. 
