R. Arnold — Rocks from the Sawtooth Range. 13 



chlorite veins. Fresh surfaces are rough or finely corrugated. 

 In thin slides, the rock is seen to have fine diabasic texture, 

 the plagioclase, which occurs in small lath-shaped crystals, 

 apparently being more important than the augite, which in 

 many instances is altered to chlorite. Small chlorite veins 

 filled with segregations of calcite and calcite masses occur 

 sparingly throughout the rock. No olivine is seen in the rock 

 although its general appearance is like many oli vine-bearing 

 basalts. 



A specimen of amygdaloidal basalt, said to have come from 

 a detached bowlder at Smith's Camp, exhibits cavities up to 

 1/16 inch (2 mm ) in diameter, filled with a soft white mineral, 

 probably natrolite or a related mineral. This rock has been 

 erroneously called " bird's-eye porphyry " by the prospectors. 



Sei'jpentine. — A peculiar fine-grained fibrous serpentine, 

 probably antigorite, occurs in the igneous area at Camp Black 

 and White. This rock is rather dark grayish green in color and 

 upon close examination exhibits segregations of a grayer shade. 

 It breaks along several systems of shearing planes, producing 

 a jagged surface. Chlorite associated with a white mineral 

 occurs abundantly in irregular veins following the fracture 

 planes. The most interesting feature of the rock disclosed by a 

 miscroscopic examination is the occurrence in it of numerous 

 skeleton crystals of olivine now entirely altered to chlorite. 

 Most of these skeletons appear as long narrow rectangles with 

 an acute, deep reentrant angle in each end. There are also a 

 few better developed olivine crystals mostly altered to calcite. 

 Radiating bunches of a serpentine-like mineral, probably anti- 

 gorite, form the groundmass. 



Ores. 



The ore samples submitted by Mr. Stanard include both 

 mineralized quartz and slate. A sample which apparently 

 came from at least 8 or 10 feet below the surface is of slate, 

 undoubtedly from near the contact with a quartz vein, and 

 contains chalcopyrite and malachite in moderate amounts. 

 Another specimen is of gray to dark reddish brown quartz, 

 containing finely disseminated free copper, and, in the cracks, 

 thin layers of malachite and azurite ; a black coating, probably 

 a hydrous manganese dioxide like psilomelane or wad, also 

 occurs prominently in this rock. A third specimen of grayish 

 to reddish drab quartz contains considerable amounts of free 

 copper with which is associated some red cuprite. These last 

 two specimens are said to be typical surface specimens. All 

 of these are from the Three Friends claim, at Camp Black and 

 White, which, according to Mr. Stanard, shows a mineralized 



