The gold occurred in a reddish oxide of iron in bunches and stringers scattered through a crushed zone of limestone, lying along the flank of the mountains. A party, who for a time was in charge of the property, informed the writer that he had worked the rock without sorting, had endeavored to sort it, and had tried screening it, but that notwithstanding every precaution was taken, he had concluded that it could not be made to pay. The gold-bearing rock was quite rich, but it occurred in too small quantity to make it profitable.
Four miles northeast of the Black Hawk Mines, lying down on the desert, is a formation of limestone and quartzite, resting on a massive crystalline rock, containing quartz, feldspar, biotite-mica, and hornblende. This reef extends from the mouth of Texas Cañon out upon the plain, sloping downward at an angle of approximately 5° for a distance of 4 miles, where it terminates in a bluff 40 to 100 feet in height. Along the entire eastern edge of this deposit it drops off abruptly as though sharply eroded. At the northern end the reef is faced by a low range of hills composed of the above-mentioned hornblende rock. From this point it swings west and with irregular outline extends for 5 or 6 miles toward Rabbit Springs. The entire area, fully 25 square miles, is cut by gulches varying from 20 to 150 feet or more in depth, that have been eroded through the strata and down into the underlying crystalline rocks. These cañons seem to have resulted from natural drainage, being started by slight depressions in the rolling plateau of limestone. On the extreme northern edge at one point, hills of considerable size have been formed by the folding and tilting of the strata. The limestone has been subjected to violent compression, as the whole area is faulted and broken into millions of fragments.
I have examined not less than twenty mining claims on the reef and traveled over the greater part of its area, and am sure I never saw a single piece of limestone that would weigh 300 pounds, most of the pieces measuring under 6 or 8 inches. Considerable masses along certain zones have been granulated, and even pulverized. This fractured rock has all since been loosely cemented by the infiltration of carbonate of lime into the seams. Geologists who have examined this peculiar deposit do not agree entirely upon its mode of formation. Some believe it to be the result of chemical precipitation of carbonate of lime from calcareous springs, similar to the Formation Springs in the Yellowstone Park. There are many things about Silver Reef which would at once suggest the probability of this mode of deposit, but I am very doubtful that such a theory will stand a thorough investigation.