As already stated, the chief rock of the surrounding country is serpentine. This is of a type common in the coast ranges and in general derived from the alteration of a peridotite. Small areas of a pyroxenic facies occur. Nowhere so far as known do the veins under discussion occur in actual contact with the ser- pentine, although it surrounds the deposit and is frequently not many yards distant from them.

The rocks immediately associated with the veins are all more or less altered, and this alteration is greatest close up to the zone of veination. In the less altered parts both igneous and sedimentary types are recognized. The more common type has in the field the usual appearance of the Franciscan greenstones. Under the microscope it is seen to have originally possessed a diabasic structure. In some specimens the augite is still largely intact. The feldspars however are recrystallized into a fine granular mass. Yet they often show very clearly by the outline of the granular areas the lath-shaped forms of the original feldspars and the relationship to the augites that characterize the diabase structure. Some titanite is present. In a somewhat altered specimen the augite is more or less altered into chlorite, while in the feldspathic layers small greenish or bluish needles are commencing to form in some cases actinolite, occasionally glaucophane, or some other geologically related amphibole. The new feldspar is at least in large part albite.

On the south hillslope below the east end of the deposit is a spheroidal gabbro. The grains and prisms of monoclinic pyro- xene are in part altered to chlorite. The labradorite is more or less decomposed and otherwise altered and the rock is impregnated with calcite. It does not come in contact with the veins at any point.

Other rocks are found having the characteristics commonly displayed by the more altered franciscan sandstones or grey-wackes. Under the microscope the light colored constituents which make up the bulk of the rock are seen to be entirely recrystallized into very fine granular aggregates. The original structure is preserved by the dark films of ferruginous or car-

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