Development work at the benitoite mine at the time of the writer’s visit consisted of a large and a small open cut, a prospect drift or tunnel with a crosscut tunnel, and an incline shaft. The large open cut or “glory hole” was 20 to 45 feet wide, 85 feet long, and from a few feet to 35 feet deep; it had a north of east direction into the hillside. The smaller open cut was to the north side of the entrance of the larger cut and at a lower level, it was about 60 feet long and 10 to 15 feet deep. The prospect tunnel was driven 120 feet in a direction N. 70° E. from the end of the large open cut. The crosscut tunnel was 45 feet long and driven to the north at a right angle from the main tunnel at a distance of 50 feet from the mouth. The incline shaft was sunk 35 feet deep from the north side of the open cut at about the middle.

The prospect tunnel cut through the hornblende schist formation into decomposed serpentine. The contact was evidently a fault line, and near it the serpentine contained much talcose and scaly asbestiform material. The fault was directly across the schistosity with a north-south strike and a. dip of 45° W. This prospect tunnel encountered a little natrolite (vein material) in the hornblende schist in its upper west side, 15 feet beyond the crosscut tunnel, which crossed a small streak of vein material containing a little benitoite about 10 feet from the main tunnel. Vein material formed the roof of the prospect tunnel for several feet near its mouth. The “glory hole” was excavated in a very large pocket or bulge in the vein, a portion of which may still be seen along the north wall of the open cut. The incline shaft was apparently sunk in the lower part of this outcrop and did not encounter benitoite. The smaller open cut exposed vein material with benitoite, which was more plentiful near the east end of the cut than at the west end. The vein and the schist in this cut were much blackened and stained with films and seams of manganese dioxide. About 30 feet S. 60° E. of the upper end of the huge open cut a ledge of altered blue hornblende schist outcrops prominently. This ledge also carries a streak of natrolite with benitoite. Benitoite has been found in bowlders a few hundred yards west of the mine on the hillside and in the creek. These bowlders have evidently rolled from the outcrop on the hill above and probably from near the mine. Doctor Louderback states that benitoite lias been found for a distance of about 230 feet at the surface along the mineral zone and in very small quantity at its extremes. The writer observed benitoite in place through a distance of about 170 feet in an east and west direction.

The strike of the ledge outcropping to the east of the open cut was about N. 60° W., with a high northerly dip. The strike encountered in the tunnel, about 30 feet lower and to the north, was nearly cast and west with a dip of about 40° N. In the upper part of the face of the open cut the dip was high, about 65° N., and below the middle of the face it was low, 15° to 25° N. Along the north side of the open cut and in the lower cut the strike was about east and west and the dip was probably rather low, 20° to 30° N. These measurements do not agree closely with those of Doctor Louderback, especially in regard to the dip of the vein. Jointing of the rock and the irregular nature of the vein, however, make accurate measurements difficult. Doctor Louderback places the dip at 65° to 69° N., but the dip measured by the writer is much lower, probably 15° to 30° N. in the lower part of the cut. The evidence for this measurement is found in the position of the vein at the outcrop and in the tunnel, of the layers of blue schist and natrolite in the end of the cut, and of the ledge along the north side of the open cut and in the lower cut. Such a low dip would account for the failure of the incline to cut the mineralized zone. The failure might also be due to the pinching out of the vein a short distance below the large pocket opened in the “glory hole.” The impression gained by a study of the deposit and by plotting the location of the vein where encountered in different places was that the deposit consists of an ore shoot pitching to the west and lying in a fracture zone in hornblende schist with an irregular east and west strike and north dip. This shoot had a lenticular cross section with a thickness of more than 25 feet in the thickest part but pinching out on the sides. The upper edge of the shoot has been removed by erosion. A portion of the lover edge was encountered in the tunnel. The eastern extension of such a shoot would have been removed by erosion and the western extension would be underground, to the north of, west of, and below, the open cut.

Doctor Louderback mentions the outcrop of spheroidal gabbro on the southeast of the benitoite deposit on the hillside. The outcrop of rock on the north side of the vein zone, on the summit of the ridge, is of a similar nature and has been mentioned above as diabase or gabbro. The same rock was encountered in the crosscut tunnel 40 feet below the surface and 30 feet north of the main tunnel. Underground this rock occurred in large loose spheroidal bowlders ranging up to several feet in thickness, with large openings between them. This material was difficult to mine and required careful timbering. The open spaces evidently extended to the surface above, as a strong draft of air came through them. The spheroidal shape of the blocks and the open spaces between them were doubtless formed by decomposition and leaching along fracture planes.