12() CONTRIBUTIONS TO ECONOMIC GE3LOGY, 1902. [bull. 213. 
Creek. With these exceptions there are no irregularities in distribu- 
tion of the Triassic and Carboniferous limestone to indicate folding or 
faulting on a large scale, although small gentle folds and faults are 
common along the limestone front in each case. The Devonian 
limestone is so cut by igneous rock as to afford no decisive evidence. 
The geological date of the folding and faulting accompanied by 
much crushing of the rocks was at the close of the Jurassic, when the 
Sierra Nevada and the Klamath Mountains were formed and raised 
above the ocean to initiate an epoch of vigorous erosion represented 
by the unconformity between the Cretaceous and Jurassic. The 
epoch of rock crushing gave rise to the shear zones which later became 
the seat of circulating waters and finally the ore deposits of to-day. 
AFTERTHOUGHT DISTRICT. 
The Afterthought district is very small. It lies near Cow Creek, 
where the copper-bearing rocks run under the later lavas from the 
volcanic ridge north of Lassen Peak. 
The country rock is chiefly igneous metarhyolite, and cuts Triassic 
slates, with large limestones near by. The ore bodies, which are 
chalcopyrite with other sulphides, as far as may be judged from sur- 
face openings — the tunnels, long unused, have caved in — occur near 
the contact between the two rocks without additional evidence of 
contact metamorphism. The adjacent rocks show extensive iron and 
copper staining. The conditions here appear to be similar to those 
of Bully Hill and Iron Mountain districts, but the extensive prospect- 
ing of years ago failed at that time to develop a paying mine. 
Later improvements in smelting low-grade ores may have changed 
the status of this property. 
BULLY HILL DISTRICT. 
Lor"/ inn and extent. — The Bully Hill district lies about 15 miles 
directly north of the branch railroad at Bellevista. It has a length 
of several miles in a direction a little east of north, and embraces not 
only the openings in Bully Hill, but also those about Copper City. 
Some openings on the slope of Horse Mountain might here be included, 
but at present the prospects, although in the same volcanic masses, 
are not sufficiently extenswe to furnish good ground for judgment. 
It is especially interesting, however, to note that Horse Mountain is 
the only locality in the region where native copper was found in the 
comparatively fresh-looking igneous rock. 
Country rocks. — The common country rocks are wholly igneous, j 
generally metarhyolite, rich in porphyrinic quartz like that of Bully | 
Hill, of which an analysis by Dr. E. T. Allen is given below (1). Some 
of the rock is metabasalt without porphyritic quartz. This is espe- 
cially the case in the Bully Hill mine, where the rock most intimately 
