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Show 14 ical work of the survey, connection with the stakes or other marks is had when practicable, and minor details of roads, trails, rivers, creeks, lakes, spriugs, & c, can be introduced from the Laud- Office plats with sufficient accuracy. The details gathered the past season are sufficient for the construction of sheets of the area occupied upon a scale of one inch to four miles, while a portion of the so- called San Juan mining- region, intricate in topography, and likely to become of importance through its mining prospects, will be mapped upon a scale of one inch to two miles; indeed, for a clear and vivid representation of the rugged wilderness of mountains lying in Southwestern Colorado, no scale less than one inch to one mile is adequate. NOTE.- The field- work of 1674 completes the connection of the areas of New Mexico and Colorado over which the surveyed portions were partially joined in 1873, while at the close of the season of 1875, the areas mapped will stretch in a belt from the Pacific Ocean to the eastern base of the Rocky Mountains, or westward from the Pecos to the Pacific. The area embraced during the past season has not been so large as in former years. Another step has been made in the direction of a more perfect and refined geodetic survey; and the system once established, the results as to areas mapped in a manner that will require no future change, except in details incident to the development of the country, will vary, the force remaining constant, according to the physical construction of the ever- shifting panorama of mountain, valley, and plain found along each parallel of latitude within the longitudinal limits of the survey. NOTE.- The number of sheets, 19 by 24 inches, required to express the topography of the United States, excepting the Alaska addition, lying west of the one hundredth meridian, upon a scale of one inch to one mile, is approximately 6,000. If each of the 95 sheets projected to form tbe atlas of that area upon a scale of one inch to eight miles were complete, the number would be 6,080 sheets. When practicable, initial monuments, marking a point of determinable position as to longitude, latitude, and altitude, the meridian- line through which has been laid out, have been erected in mining- camps about to be opened, aud where surveys of the mineral- lands, and other surveys, both superficial and underground, are about to be made. More attention will be given from year to year to the selection of points of initial value in the future survey of the mountain- ranges in greater detail, or those portions of them from which the precious and other metals are to be extracted. It would appear eminently proper to anticipate, since this work lies outside and in advance of the Laud- Office surveys, the wants of this class of surveys at the time that they shall be extended largely into the more impassable mountain- sections, so that in the future the linear or rectangular connection over difficult lines may be avoided, or perhaps replaced by a triangular system to be made applicable to all classes of areas within the western mountain- regions. From time to time, as mineral development on a large scale has brought to light a knowledge of the circumstances of ore- deposition in veins showing considerable permanence, and from which large annual products are obtained, more minute topographical surveys should be prosecuted, and the superficial and underground relations between the source of mineral- supply aud the u country- rock" be obtained. In this connection, the plane- tables and other instruments convenient for the determination of contours over medium- sized areas will be brought into requisition. In volume I will appear a clear and full exposition of the. principal |
