130 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
in prospecting about Bully Hill and the great volcanic belt extending 
north to Bollibokka Mountain. Prominent limonite deposits from 
iron springs strongly suggesting gossan beneath were seen at several 
points a short distance northeast of Bully Hill, on the area of Triassic 
slates. The slates along the contact with the volcanics are in places 
richly impregnated with pyrite, but thus far no mines have been 
opened. This field is well worthy of careful prospecting and is now 
receiving attention, for recently much work has been done on some 
claims near Bollibokka Mountain. 
BLACK DIAMOND DISTRICT. 
The Black Diamond mine, which was practically closed in 1002 
except for a small amount of prospecting, is about 20 miles northeast 
of Redding. It furnishes an excellent example of ore deposits on or 
near the contact between limestone and diabase. The relations of 
the deposits in this district differ widely from those of the other dis- 
tricts. The limestone and associated sediments are well characterized 
by fossils of Carboniferous age. 
Small masses of pyrrhotite a and chalcopyrite occur, also pyrite and 
magnetite with limonite and other secondaiy minerals. The ore is 
associated with coarsely crystalline green fibrous pyroxene and gar- 
net, whose relations are not so easily perceived in the mine workings 
underground, but upon the surface are illustrated at many points in 
the neighborhood along contacts of diabase dikes which cut the lime- 
stone. The best exposures are upon the crest of the limestone ridge, 
where it is crosscut by a number of diabase dikes running east and 
west and ranging from 5 to 100 feet in width. Along the edges of 
these dikes in contact with the limestone at many points pits have been 
dug into the iron-stained fibrous masses of pyroxene mixed occasionally 
with garnet, serpentine, and traces of ores. The fibers of pj 7 roxene 
several inches in length are perpendicular to the contact and are 
conspicuous. Numerous open cuts and tunnels have been made in 
connection with the Black Diamond and Roseman group of mines. 
All were not examined, but as far as seen the relations were all 
essentially the same as described above. 
The dike rock in question, here designated diabase, is composed 
largely of calcic feldspar, which generally has the ophitic arrange- 
ment characteristic of diabase, and incloses chlorite, epidote, magne- 
tite, and quartz resulting from the alteration of feldspar and pyrox- 
enes. The amount of quartz varies, and in some cases it seems a 
primary constituent. 
These contact deposits have been exploited chiefly about Grey 
Rock, and to a less extent north of Pit River, where work is now 
progressing in an open cut, iron ore being taken out for flux at the 
Bully Hill smelter. The mass of magnetite incrusted by limonite is 
"The pyrrhotite was examined for nickel, but there is none present. 
