50 
CORUNDUM IN THE UNITED STATES. 
[BULL. 180. 
The crystals are usually rough and more or less striated, so that no 
measurement could be made upon the reflecting goniometer, but suf- 
ficiently accurate measurements could be obtained with the contact 
goniometer to identify the faces. 
The largest crystal that has been observed from any of these bars 
was one from Eldorado Bar that was nearly an inch long and three- 
eighths of an inch in diameter. 
A repeated growth was observed on some of these crystals, but not 
in the variety of forms seen in the Cowee rubies (p. 43) and the Yogo 
Gulch sapphires (p. 52). Only one form of growth was observed, repre- 
sented in fig. 9, A, which is a combination of the unit rhombohedron 
and the base. 
Since the discovery and mining of sapphires from the Missouri 
River bars sapphires have been found at three other localities in Mon- 
tana — at Rock Creek, Granite County; at Cottonwood Creek, Deer- 
lodge County; and at 
Yogo Gulch. 
Fergus County. 
The first two localities are about 80 and 30 miles southwest of those 
on the Missouri River, and the last one is about 80 miles to the north- 
.4 B C 
Fig. 0.— Sapphire crystals from Missouri River bars, Montana. 
east. From these sapphire deposits stones of deeper colors have been 
obtained, those from the first two being of all colors from blue to red, 
while those from the last are all blue. 
ROCK (REEK SAPPHIRES. 
For informal ion concerning the sapphire deposits of Rock (reck, \ 
am indebted to Mr. William Knutli, of Helena, All the sapphires 
that have thus far been found in this section are in the gravel deposits 
on the West Fork of Rock or Stony Creek, in the southern part of 
Granite County, about 35 miles southwest of Phillipsburg, the county 
seat, and 30 miles nearly west of Anaconda, Deerlodge County. 
(PI. IV.) 
The sapphires are found in rather a limited area, which is bounded 
roughly by the gravels of Cold Creek, Myers Creek, tributaries of the 
West Fork of Rock Creek, and that portion of Rock Creek lying 
between them. 
These gravels were extensively worked during the summer of IS!)!), 
principally by William Knuth, of Helena, and William Mofifitt, of 
Phillipsburg. Altogether about 200,000 carats of rough sapphires 
