lindgken] BITTERROOT AND CLEARWATER MOUNTAINS, MONT. 67 
Along the whole eastern slope of the Bitterroot Mountains this 
granite is made schistose by pressure, and forms a zone a few miles 
in width and 60 miles long, following the front of the range. A great 
fault accomimnies this schistose zone, dipping, like the schistosity, 
about 18° E. Otherwise the granite is generally massive and but 
little altered. Several smaller areas of a much older gneiss (pre- 
Cambrian?) occur in the Clearwater Mountains, the largest appearing 
near Elk City. The granite is intrusive in this gneiss. Along Lolo 
Fork at the northern end of the Bitterroot Mountains and near the 
head of the Bitterroot River are areas of quartzites and slates (prob- 
ably of Cambrian or pre-Cambrian age) into which the granite is also 
intrusive. Finally, along the western foot of the Clearwater Moun- 
tains, near Harpster and Mount Idaho, occur slates, limestones, and 
greenstones, which continue, with a northeasterly strike, up from the 
vicinity of the Seven Devils and the Lower Salmon River, and which 
are believed to be of Mesozoic age. Into this series, also, the granite 
is intrusive. 
The main structural features consist of the great Bitterroot fault 
and the uplift of the Clearwater Plateau. There is some evidence of 
comparatively recent movement along the former, although faulting 
is believed to have begun along that line in pre-Miocene times. The 
latter uplift is of pre-Miocene age. 
ECONOMIC GEOLOGY. 
Character of mineral deposits. — The valuable mineral deposits 
occurring in the area described in this report consist chiefly of Assure 
veins containing gold, together with associated placers derived from 
the disintegration of the veins. Deposits containing lead and copper, 
and usually silver, occur also in several isolated places. Coal of a 
fair quality has also been found in the upper Bitterroot Valley and 
in the lower Clearwater drainage. The lead-silver veins of the Coaur 
d'Alene Mountains are outside of the limits of this reconnaissance. 
Distribution of deposits. — The metalliferous deposits are grouped in 
two belts, the first along the western side of the Bitterroot Mountains, 
chiefly in Montana; the second along the western foot of the Clear- 
water Mountains in Idaho. The deposits of each of these two belts 
are again grouped principally in two regions forming the four corners 
of the mountain area involved, while the central part of the Clear- 
water Mountains appears to be practically barren. The four metal- 
liferous areas are distributed as follows: The first occupies the lower 
Lolo Fork and the northern end of the Bitterroot Mountains; the 
second is found on the headwaters of the South Fork of the Bitterroot 
River and reaches over into Idaho, connecting with the mineral belts 
at Shoup and Gibbonsville ; the third and most important area includes 
Elk City, Buffalo Hump, Dixie, and Florence, as well as numerous 
places along the South Fork of the Clearwater River; the fourth area 
