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Show APPENDIX NN. 1285 of the vein, and also of the conn try- rock, has on the whole increased, or, at all events, high temperatures have become more common as the workings gained in depth. Observations on this point have been collected, and a system will soon be instituted which, it is hoped, will afford valaable information upon the best means of overcoming the heat of the mines. The deep adit called the Sutro Tnnnel has penetrated about 17,500 feet, and is now abont 2,750 feet from the lode. It is advancing at a rate of speed which shonld take it to the vein about March, 1878. It will, however, reach the line of the deep shafts sunk in the east country rock some time next month. Its completion cannot fail to have imporrant results upon the drainage of a vein that is liable to sudden outbursts of wa'er in great quantities, as the Comstock is. The milling of the ores has undergone some alterations, but nothing so extensive as those above indicated in the mining. The latest- built mills are models of convenient arrangement and economy. On the whole, the ore which is now extracted is richer than auy which has been obtained since the earliest period of mining on the Comstock vein, and the problem of milling these ores with as high, or a higher, return as was formerly obtained from less- rich ores has been successfully grappled with. I have thus sketched, in a very general way, the condition of the field to which I am assigned. My work so far has consisted in preparing for the observations necessary to a study of the ventilation and drainage of the vein and the position of the ore- bodies fonnd below the 1,000- foot levels. I have great pleasure in acknowledging the courtesy and frankness with which every one connected with the mines has received me. No restraint has been placed upon investigation, but, on the contrary, the survey can count upon the active co- operation of the mining companies, even at some trouble and cost to themselves. I am, very respectfully, yours, JOHN A. CHURCH, Alining Engineer. LIEUT. GEO. M. WIIKELER, Corps of Engineers, in charge. APPENDIX H. GEOLOGICAL REPORT ON THE PORTIONS OF WESTERN NEVADA AND EASTERN CALIFORNIA BETWEEN THE PARALLELS OF 39° 30' AND 33° 30', EXPLORED IN THE FIELD-SEASON OF 1876, BY MR. A. B, CONKLIXG. NEW YORK CITY, Jpril 16,1877. SIR: The area examined is bounded on the north by a line drawn through Truckee, Cal., and Washoe City, Nev.; on the east by the Mount Davidson Range and theComo Mountains; on the south by Job's Peak and Pyramid Peak; and on the west by the Western Summit and the Truckee River. Nearly all of this region is covered by granite, with occasional outbursts of basaltic rocks. No fossils are found except at the State prison quarries, one mile east of Carson City. There is abundant evidence of the former existence of glaciers in the mountains bordering Lake Tahoe. Thermal and mineral springs occur in several localities. A few ore- deposits are found within the area explored in 1876, but only one of them possesses sufficient importance to deserve more than a passing notice. Two ridges, running north and south, traverse this section of country. They are termed the eastern and westeru summit'*. Lake Taboo separates the one from the other. The latter range is more broken up by precipitous canons and minor ridges than the former. Both the summits are sparingly wooded, from the base to the crest- line, and may be regarded as parallel lines of elevation. Having given an account of the general features of the area explored in 1876,1 now propose to take up the geology in the following order: 1. Description of the Carson Valley and vicinity. 2. Sketch of Lake Tahoe. 3. The eastern summit. 4. The western summit. THE CARSON VALLEY. There are several thermal springs in the Carson Valley within a radius of abont fifteen miles of the capital of Nevada. The most important spring rises in yellowish sandstone about a mile east of Caison. The temperature of the water is 111 degrees F. A bath- house has been erected at the springs adjoining the State prison. Another hot spring occurs in mica slate 2£ miles northeast of Carson. The water is clear and has a temperature of 120 degrees F. There are several wells about 10 inches deep in |