wright.] GEOLOGY. 17 
pine, and as the intervening rocks are unknown, a correlation of the 
sedimentary formations in the two ai*eas is hardly advisable without 
more thorough investigation. 
INTRUSIVES. 
The rock of the Coast Range intrusive belt in this region is mainly a 
coarse-grained diorite of a light-gray color, composed of plagioclase 
feldspar, hornblende, some biotite, and a little quartz, though speci- 
mens collected from different places vary in composition. The main 
mass north of Klehini River corresponds with the description above. 
The narrow belt at the head of Porcupine Creek contains more biotite, 
and segregations of hornblende and mica are often prominent, causing 
large dark spots, which are locally characteristic. The continuation 
of this belt to the east at Cottonwood Creek is characterized by a 
microcline feldspar and a larger amount of quartz. Under the micro- 
scope some of the minerals are seen to have" been crushed, indicating 
that since the intrusion of the diorite they have been subjected to 
pressure and movement. This diorite rock is locally termed granite, 
which it resembles very closely and from which it can be distinguished 
only by careful examination. 
In the central part of the sedimentary series there are several cross- 
cutting greenstone dikes, averaging 10 feet in width and often trace- 
able for several hundred feet. They are green in color, fine grained, 
often porphyritic, and under the microscope were determined to be 
altered diabase, occasionally mineralized. The relative ages of the 
diabase and the diorite could not be determined, as the two were not 
found in contact. 
On the north bank of the Klehini, seemingly interbedded in the 
slate, there is a greenstone schist forming a bed about 40 feet wide. 
Aside from this no schists were observed in the district. 
MINERAL OCCURRENCE. 
The sedimentary rocks have all been more or less mineralized by 
stringers and veins of quartz and calcite, but an especially noteworthy 
impregnation of iron sulphides forms an interrupted zone of mineral- 
ization in the southern portion of the sedimentary series. The sul- 
phides in the slates occur as films or frequently as lenticular masses a 
few inches in width, parallel with the bedding. Two samples of the 
mineralized slates, one an average across several feet and the other 
from a rich seam, gave respective^ $0.41 and $2.48 per ton in gold. 
Samples from near the mouth of the Porcupine, where the slates are 
apparently unmineralized, taken by Mr. Brooks during his short visit 
to this region in 1899, a gave traces of both gold and silver. 
a Brooks, Alfred H., op. cit., p. 374. 
Bull. 236—04 2 
