Louderback, G. D. "Benitoite, Its Paragenesis and Mode of Occurrence." University of California Publications.
Page 339
over the natrolite, and disfigured its shining pure white surface. The general dark areas in plate 29 are due to limonite films. Fortunately, the benitoite and most of its associates are very resistant to weathering, and besides they are generally well enclosed in impregnated blocks that shed the water into their more porous neighbors. Plate 32 is a more general view of the face of the cut, and the distribution of vein-stone can be there better followed. The rope lies on the fault-plane, and to its right is the sheeted greenstone. Starting from the curve in the rope, to the left a number of harder blocks are to be seen lying almost on a level. These are all "ore". Above them is a greenish blue, porous, highly altered country, characterized by an extensive development of green to blue amphiboles. At the left edge of the photograph is a large mass extending to the floor of the cut. It is evidently a breccia, and is highly impregnated. It also is "ore", if in part low grade. This mass extended out originally into the cut, where it was separated from the vein-stone in the face as a result of a transverse fault. The zone here dips to the left. Its irregularity is evident. The highest visible point of the rim is thirty-seven feet above the floor of the cut.

We may consider briefly the practical bearings of these postveination movements. They have increased the difficulty of mining by producing irregularity and discontinuity of the gembearing matrix, by leaving the rock in a weakened condition so that movement and caving are always imminent, and by affording ready access of surface water into the workings. The workings are at present so shallow that there is not sufficient evidence on which to base an opinion as to whether these conditions will change or not with increasing depth.

SIZE AND ATTITUDE OF OUTCROP.

The outcrop of the mineralized zone is not very extensive. At its widest point it is about sixty-four feet. Its length is not over four hundred feet. Of this the easternmost part carries barren natrolite veinlets and thewall-rock shows a minimum of metasomatic alteration. Benitoite has been found at the surface along only about 230 feet of the zone, and at the extremes of this distance only in very small quantity.

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