BO? E. P. CAREY AND W. J. MiELER 
tially of diallage, the latter presenting an uneven fracture, while the 
former is a compact rock with a conchoidal fracture. 
The mesh structure is common, especially in the compact con- 
choidal variety, while grains of olivine and minute crystals of mag- 
netite are disseminated throughout the whole mass. ‘The minute 
crystals of magnetite may be detected in the groundmass by the aid 
of a pocket lens, and are so numerous that the fine powder of the 
crushed serpentine will immediately jump to a magnet. ‘These 
magnetite crystals are chiefly concentrated along the lines common to 
contiguous meshes, but are at times also found along with serpentine, 
making up dark anastomosing veins, attaining in some instances 
half an inch or more in width. 
Genesis of serpentine from peridotite.—The structure and miner- 
alogical composition of this serpentine then clearly indicate that it 
was derived from a basic rock in which olivine was the predominating 
mineral together with diallage and magnetite. The peridotite from 
which the serpentine was derived is not found in a fresh condition. 
It is interesting, however, to note that in the phases of the rock in 
which diallage predominates we do have a comparatively fresh noes, 
which fact confirms the igneous origin of the serpentine. 
Chromite.—Several somewhat irregular pockets of chromite in 
peridotite-serpentine occur in the Los Lagrimas Hills, never exceeding 
a few feet in extent. The relative hardness of the ore in some cases 
caused it to stand up above the surrounding surface. On this account 
it attracted attention, and formerly on the Swickard ranch near the 
Coyote Creek, these occurrences were mined, and the product shipped 
east. So intimately associated is the serpentine with the chromite 
that it is difficult to secure from these prospect holes a hand specimen 
of the ore that does not contain serpentine. It would seem as if the 
chromite is a product of differentiation from the serpentine. 
Cinnabar.—The San Juan cinnabar mine occurs on the Oak Hill 
area. Here the ore occurs along joint planes and zones of faulting, 
the impregnations extending some distance from the walls into the 
serpentine and its alteration products. Extensive mining is not now 
carried on in this region, though operations are now being conducted 
in a small way. 
At the Silver Creek mine, four miles south of Evergreea, in appar- 
