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Show 1 2 5 8 REPORT OF THE CHIEF OF ENGINEERS. traversed by the Geiger grade, and that to the east embracing the basin between Monnts Emma and Davidson. Dr. Kainpf, after finishing the base measurement, went to Virginia City and determined the azimuth of the triangulation lines from the astronomical monument, a n d on October 23 started for Washington. Mr. Seckels joined the party in Virginia City and devoted himself with assiduity and intelligence to the necessary meteorological work. November 20, I received orders to proceed to Carson City to disband for the season, where I arrived November 23. After spending two weeks in Carson, seeing t o the storage and shipment of public property, taking inventories, and acting as member of a board of survey, I started for Washington on the 5th of December. In obedience to verbal orders from Lieut. S. E. Tillman, in charge of disbanding the California section of the survey, I stopped at Ogden, Utah, and made an inspection of the Government observatory there, and an inventory of all the public property pertaining to the expedition, the reports of which have been submitted to Lieutenant Wheeler. On my arrival in Washington I was placed in charge of the meteorological records and computations, and also to supervise the compilation aud reduction of the plane-table work. I have carefully recomputed all the positions used in the held and several others, which will give the foundation for the work when it is next taken up in the field. DESCRIPTIVE REPORT. The area embraced in the contemplated and partly constrncted detailed contour map is 12£ miles long from north to south and 9+ miles broad from east to west, and contains within its limits the richest mines of silver and gold of which the world of to- day has any knowledge. About 12 miles to the east of the summits of the Sierra Nevada Mountains, a little northeast of Lake Tahoe, iu the niidtt of piled- up masaes of volcanic rocks of all kinds, where during the summer rain never falls, and where nothing grows but sage- brush ; where the mind of man can imagine nothing to add to the scene to make it one of more cheerless grandeur and desolation, is situated the famed Comstock lode. Above the lode and its branches have been built the towns of Virginia, Gold Hill, Silver City, and American Flat, in which are situated the upper works of the mines and their many adjuncts. Immediately connected with it by virtue of their ore mills are the towns of Dayton and Empire, and from being the outlet of the Sntro Tunnel is the town of Sutro. I shall not attempt to describe these places in detail, but shall simply note some observations of my own and some of the changes which have taken place since other reports have been written, and which are continually taking place. At the time when Mr. Clarence King wrote his report upon the geology of the Comstock, it was considered that the portion of the lode bet wee u- the Gould and Curry, and the north line of the Ceutral, corresponding to the south side of the Ophir, was unproductive, and from the apparent closing in of the walls it was supposed that ft never would develop into anything of much value. Since theu, however, under the names of the Consolidated Virginia and California, this region has developed the Big Bonanza mines, one, the Consolidated Virginia, yielding in the year 1875 alone the enormous amount of $ 16,731,653.43 from 169,095 tons of ore. This is a gigantic illustration of the fact that the vein is very unreliable, and that it is not safe to place very much reliance on analogical reasoning with regard to it. The old controversy as to there being a single vein of which the outlying ones are branches or spurs is still unsettled, but agencies are at work now which will, in all probability, settle the question at law in a few years at the farthest; these agencies being particularly the Sutro Tunnel, the Mint Mine, and the Great Combination shaft. In the report of Mr. Ring the Comstock lode is supposed to extend approximately north and south from the vicinity of the Utah Mine, to the mines in and about American Flat, and no mention is made of a branch lode extending down Gold Canon. It is generally conceived now that the great lode branches near the head of Gold Cafion, and one branch extends southwestward toward and beyond the Rock Island Mine in American Flat, and the other extends southeastward down the ca& on. Some of the most promising and productive mines of all the region are situated in this latter branch, notably the Overman and the Justice, which have both big bonanzas, the latter especially working some very rich ore, of which a specimen now in this offio assays approximately $ 12,000 per ton. Prospecting and exploitation are still going on in a great many places, both on the lode and off it, and the horizontal limits of pay- ground is not yet reached, or at least is far from being determined. But many things would go to show that the vertical limit of successful working has been reached in some of the mines as long as the present system prevails. In the Savage Mine, nearly or quite a year ago, as a drift was being pushed to the east at a depth of 2,300 feet, a heavy volume of hot water was encountered which drove the workmen back and up the shaft, and, in spite of the pumps, continued to come in until it reached the 1,900- foot level. Since its first influx larger and more powerful pumps have been put in and kept at work continuously except for accidental stoppages, and at last accounts the water was still at about the same level. Although at times the pumps would gain on the water, the water would in a short |
