Congressional serial set Volume 2051

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1882 Excerpt: ...less than 400 feet from the surface, indicating an extensive body still farther east. The lithological varieties of the diabase have been sufficiently described in a former chapter. In structure it resembles the diorite, being split up near the Lode into rough sheets parallel to the main fissure, as has been explained in Chapter IV. I have been wholly unable to see any evidence that this rock was not emitted at a single outbreak. Its position, lying as a mass upon a diorite wall sloping at an angle of about 45, together with the details of the relations of the two rocks, shows that it is younger than the diorites. That it is also probably younger than the quartz-porphyry is shown by the occurrences in the Overman, which are not fully satisfactory only because they are so limited. Biack dike."--The younger diabase, as has been seen, is identical with the trap of New Jersey. It has often been confounded with the black slates of the Gold Hill mines, and black rocks and clays have sometimes been classed with it in the north end mines. In the upper levels it was met with only in an indistinguishably decomposed form. I was not able to authenticate its occurrence north of the Savage, and found it, wherever struck, of a very uniform width, always a few feet, never more than a couple of yards. From the Savage to the Overman it generally marks the contact between the older diabase and the west wall with precision, but on one level of the Chollar it is 80 feet west of the contact, and in the Yellow Jacket a narrow belt of slate sometimes lies east of it. In the Overman the dike diverges from this contact, extending towards American Flat as far as the Caledonia. The uniform thickness of the dike shows that no considerable movement between the diabase and the west ...