72 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
beds consisting in the upper part of shales and limestones, but includ- 
ing, at lower horizons, tuffaceous sediments and flows, which have 
an aggregate thickness of 6,000 or 7,000 feet. Many basic igneous 
masses occur as dikes or intrusive sheets in these sediments. They 
are especially abundant near the fault. The shales are slightly meta- 
morphosed in the vicinity of Slate Creek and Miller Gulch, where 
some cleavage has developed and a few quartz stringers are found 
cutting them. Eocene lignite-bearing beds occur here and there in 
small patches infolded with the Permian. 
South of the Permian belt occurs a complex terrane of older rocks, 
consisting of conglomerates, quartzites, tufaceous beds and probably 
flows, which appear to be faulted against the Permian. This terrane 
is intruded and altered by dikes and greater masses of granite and 
quartz-porphyry. One effect of the intrusion and alteration is a gen- 
eral impregnation by pyrite, whose oxidation products color the rocks 
rust -red and render them especially conspicuous. 
In addition to these easily separable consolidated rock masses, 
unconsolidated cla}^s and gravels, either primarily or secondarily of 
glacial origin, occur in the vallej^s generally. Near the sources of 
the streams these deposits are confined to flood plains or narrow bor- 
dering terraces, but downstream the area covered by them widens, 
until it merges with the broad drift-filled valley of the upper Copper 
Basin, from whose borders isolated bed-rock areas rise as islands. 
Besides these Pleistocene deposits in the lowlands, a thin sheet of 
cobbles, called by the prospectors the " round wash," is conspicuous 
on the hilltops about the head of Slate Creek, Miller Gulch, and some 
of the tributaries of the upper Chesna. 
GOLD OCCURRENCES. 
Practically all of the gold mined at present is taken from Miller 
Gulch, Slate Creek, and the Chesna River, whose combined yield for 
1 91 >2 is estimated at $225,000. Of this amount, Miller Gulch probably 
furnished $175,000, Slate Creek $30,000, and Chesna River $20,000. 
Miller Gulch, whose yield is thus seen to be much greater than that 
of any other stream in the district, is a steep ravine, less than a mile 
long, tributary to Slate Creek. Its bed, decreasing in width from 200 
or 300 feet near its mouth to but 4 or 5 feet near its source, is sheeted 
over with gravel to a depth of from 4 to 8 feet. This gravel is com- 
posed principally of fragments of the somewhat metamorphosed Per- 
mian shales in which the ravine is cut, but has an admixture of diabase 
and " bird's-eye porphyry " from the intrusives in the shale, and of 
cobbles from the "round wash" which occurs over the tops of the 
adjacent hills. The gold is rather uniformly distributed across the 
gulch, but vertically exhibits the usual concentration near bed rock. 
The richness and shallowness of the gravels, and the steep gradient 
of the stream, giving abundant fall, have made it easy to win the 
