. Annual report. 1st-12th, 1867-1878. Geology. 178 GEOLOGICAL SURVEY OF THE TERRITORIES. The dike is in the same mountain, not more than three hundred yards from the Gregory lode. It is exposed by an artificial cut for a road up rig. 20. the side of the mountain, and but for this circumstance would, not have been visible from the surface. It is vertical, twenty feet high, and three to four feet wide. The materials in- closed in the dike are evidently very old basalt, yellow buff color, with cavities filled with decomposed feld- spar. The country rock does not ap- pear to have suffered changes,
. Annual report. 1st-12th, 1867-1878. Geology. 178 GEOLOGICAL SURVEY OF THE TERRITORIES. The dike is in the same mountain, not more than three hundred yards from the Gregory lode. It is exposed by an artificial cut for a road up rig. 20. the side of the mountain, and but for this circumstance would, not have been visible from the surface. It is vertical, twenty feet high, and three to four feet wide. The materials in- closed in the dike are evidently very old basalt, yellow buff color, with cavities filled with decomposed feld- spar. The country rock does not ap- pear to have suffered changes, but the lines of bedding are entirely inter- rupted,- and curved upward. The following notes on the Sweet- water Mines were taken by Mr. Ar- thur L. Ford, the mineralogist of the expedition: Dyke, near Central city^ Cariso Mines.—Worked by Mr. Colorado. Eoberts, of South Pass City. Shaft one hundred and forty feet deep, sunk in vein of very refractory quartz- ite averaging four and one-half feet in thickness; strike of vein north- west and southeast, with dip of 70° to northeast. Cap rock and wall rock consist of tough gneissoid slate containing a little free gold, and occasionally showing a few small cubes of iron pyrites. The gold con- taining the quartz is very finely disseminated, but is " free " and very pure, and hence easily amalgamated; it contains about one-half ounce of silver. About four tons of ore are being taken out daily, with an average yield of $75 per ton, and sometimes doubling that amount. The quartz is of remarkably even quality, seldom falling much below the average yield. Mr. Roberts estimates the gold already produced to amount to about $75,000. The mine makes very little water, about eight or ten buckets being taken out hourly. Young America Mine—Mr. Incath, manager. On same lode as the Cariso ; quartz contains considerable disseminated oxide of iron, but is not on that account less refractory. Ore averages about $23 per ton—not visite
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