The first rock exposed along the road to the mine east of the creek is a dark flinty one. This is followed by a body of black porphyry, with white feldspar crystals. The porphyry is about a mile across, and is followed on the east by massive black crystalline rock, and that by a felsite. These rocks are soon replaced by granite, in which there are dikes of fine-grained, highly quartzose granite. Little black veinlets of tourmaline aggregates are very numerous in the granite, extending through all the rock up to the porphyry. They have a northeast direction. The material forming them is the same as the gangue of the tin veins. A half mile south of the road is a cañon. Here the porphyry is seen extending up to the granite. The granite is greatly broken near the contact, and though there is no blending of one into the other, there is a confused mixture of broken portions of both rocks. Bunches and dike-like bodies of granite are inclosed in the porphyry. The little veinlets of tourmaline seem to have replaced the feldspar and mica, leaving the quartz. These veins grow larger toward Cajalco Hill. Just west of the works is a great mass of the black veinstone, the gangue of the tin ore. This rises in high, rugged croppings, and covers an area of about 300 by 250 feet. This is the greatest body of vein matter to be seen in the district. The tin deposit worked lies in an eastern prolongation of this cropping. The course of the veins is north 45° east, dip 65° to 70° northwest. The country rock is a coarse hornblendic biotite granite. The vein has the usual character of mineral deposits, swelling at times to a width of 8 feet, and then contracting to much less. The highest grade ore is found in the narrower portions, where it is sometimes almost pure tin oxide, running as high as 70 per cent. The vein matter does not consist wholly of tourmaline, but contains quartz grains scattered through it in about the same proportion as in the granite. The tin is not found in the quartzose part of the gangue to any extent, but in the irregular vein-like deposits of pure tourmaline, which lie in the quartzose gangue. The tin occurs in this in bunches and stringers of nearly pure ore, or disseminated through it. This is particularly the case where the width of the vein is 6 to 8 feet. Where it pinches, the whole vein is sometimes formed of the tourmaline aggregate and tin ore. The vein has usually clay seams on both walls; sometimes it is frozen to one wall; wherever the walls come together and cut out the vein matter, the seams remain. The tourmaline vein matter is an aggregate of needle-like crystals. There are two varieties of tin ore: the yellow, appearing in thin layers in an uncrystalline form; the brown, in granular form in the massive specimens, or in small, clear, reddish brown crystals lining cavities. In the latter case it forms handsome specimens. A small amount of arsenical pyrites is present in places in the vein, and iron pyrites in the granite.