FERGUSON AND TURGEON: HARNEY GRANITE. 279 
seen, only a few feet intervened between the lower outcrop of the 
Cambrian and the highest part of the Algonkian. Furthermore no 
porphyry was found between the two rocks. 
A somewhat similar case where the basal Cambrian rests on the 
granite has been described by Darton in the Bear Lodge range 35 
miles to the westward. (Darton, b., p. 5, c., p. 4.) Here a granite 
mass some three miles long and three-eighths of a mile wide is overlaid 
for the greater part of its length by the basal quartzite of the Cambrian. 
This, however, differs from the case just cited in that both the granite 
and the Cambrian bed are themselves enveloped in the porphyry. 
A possible objection to this hypothesis is that the granite and schist, 
being different from the Algonkian of the vicinity of Deadwood, cannot 
represent a part of the immediate floor on which the Cambrian was 
laid down. This objection, however, would be removed if we could 
imagine the presence of a pre-Cambrian fault between the gulch 
where the Algonkian occurs and Deadwood, bringing a different phase 
of the Algonkian to the pre-Cambrian surface — and possibly giving 
the line of weakness followed by the intruding Tertiary porphyry. 
The third explanation — that of an inclusion up from great depths — 
saves us from this rather imaginative conception of an invisible pre- 
Cambrian fault. But here again it is not easy to imagine that such a 
large block could be lifted to the very top of the domed porphyry 
reservoir and there pressed against the lower member of the Cambrian, 
without an intervening layer of previously solidified porphyry. It is 
true that no actual contact of Algonkian and Cambrian could be seen, 
some few feet of talus intervening between the nearest outcrops, but if 
there were porphyry between, it should stand out in a ledge, being 
one of the most resistant rocks of the region. 
The absence of granite pebbles in the basal conglomerate of the 
Cambrian in the Whitewood canyon laccolith, tends to support this 
explanation. But as the conglomerate was only found in two places, 
this is not very significant. 
To sum up, from the available evidence, the origin of the granite 
and schist in this region: — 
The granite rests upon the Tertiary porphyry and hence its appear- 
ance here is due to the porphyry intrusion. 
It may be either a part of the floor on which the Cambrian was laid 
down, broken off from the wall of the conduit and carried up with the 
porphyry, or it may be an inclusion in the porphyry magma, brought 
up from great depths. 
The Porphyry Sills. 
Porphyry sills were found throughout the 
