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Show 1246 REPORT OP THE CHIEF OP ENGINEERS. It does not seem practicable to avail of any new pass for a through western line of railroad between latitude 35° and 40°, except that at the head of Pass Greek, a southern branch of the Huerfano that heads near the source of the Sangre de Gristo Greek, and where, by means of tunneling, a transit of the summit should be made, at an elevation not exceeding an altitude of approximately 9,100 feet above sea- level. NATURAL RESOURCES. Upon the sheets in colors, showing the natural distinctions of the surface occupied, the following divisions are made: 1. Arable.- This refers to soil susceptible of cultivation by the - use of water, when it is apparent that the supply is adequate, assuming that irrigation is necessary. 2. Grazing.- Of the various grades, often infringing upon the timbered area. 3. Timber.- The gradations in amount, size, and quality cannot be shown. 4. Arid and barren.- This embraces that part of the surface absolutely valueless for agricultural purposes, and includes desert wastes and rock exposures. The positions of mines in place and placer are at present shown only on the regular topographical sheets. The topographical sheet upon which these divisions are marked is a reproduction from the original sheets regularly issued. A legend is attached to the case of maps, giving the geographical locality of each. A description, supplemented now by the maps themselves, of sheets 61B, 610c, 65D, 70A, and 700, is given in the last annual report. BAROMETRIC ALTITUDES. Work in the meteorological branch has been confined principally to the taking of observations with a view to their subsequent computation and determination therefrom of differences of altitude between known points and those at which original observations have been taken. Good progress has been made. The altitudes are at once used in the construction of the mountain parts of the map, and upon the atlas- sheet the altitudes of the principal settlements and other marked points are noted, while from time to time the altitudes of prominent peaks and other natural objects will be published in list form. The Signal- Office, through the courtesy of General Albert J. Myer, Chief Signal- Officer, has kindly furnished transcripts of observations taken at a number of stations contiguous to the field of survey. MINING INFORMATION. Fifteen districts have been visited and located by the several parties. The cursory examination that may be carried out hastily, in a district usually not long discovered, has been made, and the facts gathered made the subject of a report. At the Gomstock Lode, made famous from its large production of the precious metals, gold and silver, more extensive examination as to the engiueering features of its mining industry has been instituted; added to the overground survey of the contour and superficial improvements, underground examinations along profile lines separated one hundred feet are in progress, and the circumstances of the mining openings upon the various levels will be noted, and the marked features discovered will 3 illustrated graphically. The conditions of ventilation and drainage II be made a matter of special study, as well as the application of |