152 Tlie American GeolomsL March, is96 
is due to minute crystals of pyrite thickly disseminated 
through the rock. A careful panning of the decomposed ma- 
terial from various places in the beds of the canons failed to 
reveal any traces of gold. 
A similar impregnation is shown by the quartz porphyries 
which appear for several miles along the P^l 1'aso range, a 
spur of the Sierra Nevadas in the Mojave desert. Granite oc- 
curs extensively in this range about 20 miles northeast of 
Mojave. A portion of this granite, perhaps 1,000 feet long 
and several hundred wide, has been mineralized, as shown by 
its reddened surface, the color coming unquestionably from 
iron pyrites. A panning of the decomposed surface showed 
the presence of a small amount of gold. 
For many miles portions of the western slope of the White 
Mountain range show reddish tints mingled with yellow due 
to the original presence of iron pyrites, for the wash from the 
canons leading into the mountains contains quartzite and 
other acid rocks tilled with iron pyrites. 
The eastern slope of the Sierra Nevadas shows the same 
phenomenon for nearly 100 miles. The more important pyri- 
tiferous areas are confined to the acid porphyries and the 
highly metamorphosed quartzose schists and slates. They 
begin with a belt of metamorphic rocks west of Round valle} r , 
near Bishop creek, and give a most striking appearance to the 
mountains in many places as far north as Alpine county. 
The pyrite seems to be distributed through the rock, the gran- 
ite often excepted, in the most indiscriminate manner. It is 
particularly noticeable about Convict lake and in the Castle 
Peak region. 
The barren slopes of the Sweetwater range in northern 
Mono county show the characteristic red and yellow tints 
visible for a long distance. An examination of the formation 
in Ferris canon shows it to be a light colored acid rock pos- 
sessing a porphyry-like aspect and tilled with small crystals 
of iron pyrites. 
No detailed study has been given to the question of the 
origin of the iron pyrites. To the writer it seems that it must 
be of secondary origin and that it is related to the widely 
disseminated deposits of the precious metals. Its presence in 
the ancient acid eruptives as well as in the most of the varie- 
