88 The American Geologist. February, looo 
called "picrolite," serpentine, schist, diabase and black slate. 
The principal mine is The Boulders. 
2. The Lower Cofifee creek district, situate in the grano- 
dioryte batholith about 5 miles aboA'e the mouth of Coffee 
Creek. The mines are all grano-dioryte. This district is char- 
acterized by the general absence of free gold, although the ores 
are rich. The Goldon Jubilee, Wagner and Burner mines are 
the principal ones, with a half dozen or more promising "pros- 
pects" in the near vicinity. 
3- The Upper Coffee creek district, situate about 8 miles 
farther west, crosses the Coffee creek valley in the vicinity of 
the Nash store and well-known placer mine, trends thence 
nearly due south by way of the head of Pin and Union creeks,- 
then follows the main divide between the South fork of the 
Salmon river and the head of Swift creek. It has been traced 
throughout a distance of to miles and has a width varying be- 
tween one-half and one mile. The veins are very dissimilar, 
and the gold occurs in all the formations of the district, includ- 
ing serpentine, mica and hornblende schists, and the various 
intrusives including grano-dioryte. The principal mines are 
the Hardscrabble, Dorleska, and Blue Lead-Iowa, with a 
score or more of promising "prospects." As this is the coming 
great mining district of northwestern California, I shall discuss 
it in more detail than the others. 
The Mines. 
The Boulders. — A 4 to 20-foot vein of sacharoidal quartz of very fine 
texture and a nearly pure white color, occurs near the junction of 
serpentine and the underlying "picrolite." The vein trends to east- 
northeast and dips steeply to the south with the dip of the strata. A 
fault has occurred along this line and by the shearing action, a belt 
of the serpentine has acquired a schistose structure, part of which by 
metasomatic action has been converted into talc schist. This schist 
band always accompanies the main vein, and contains irregular 
stringers of gold-bearing quartz. Along the fault-plane has been 
injected a narrow dike of dioryte-porphyryte of the later system, 
which in places, carries gold to a value of $1.50 per ton. On the 
slope of Tamarack peak, a great land-slip along the schistose band 
has brokefi away the quartz vein and scattered its huge fragments 
or "boulders" over the mountain side below. The accidental dis- 
covery, some years since, that these were very rich in free gold (some 
assaying over $500 per ton), occasioned great excitement in the vicin- 
