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480 relating to problems directly affecting the study of rocks or minerals, a knowledge of which is necessary for the field geologist; a photographic laboratory, in which all negatives taken in the field are developed and prints made therefrom, and where the field topographic maps are reduced to the scale required before engraving for publication; a petrographic laboratory, which includes the necessary machinery for cutting thin sections of rocks and minerals, and for the cutting and polishing of sections of limestones, fossils, etc.

The topographic division occupies the fourth and fifth floors of the main building. This division is fully equipped with the necessary instruments for triangulation and topographic surveying. The second and third floors are occupied by the geologists of the survey, and the first floor by the administrative offices, the editorial rooms, and the library. The library at the present time contains thirty-five thousand books, fifty thousand pamphlets, and twenty-six thousand maps, all of which are intended for study and reference by the members of the survey. The administrative branch of the survey includes the chief clerk's office, the financial division, and the miscellaneous or correspondence division. In the printing division there is a full equipment for engraving, lithographing, and printing the topographic maps and folios of the survey.

The organic law of the survey, enacted in 1879, provides that "the director of the Geological Survey shall have the direction of the Geological Survey and the classification of the public lands and examination of the geological structure and mineral resources and products of the national domain." In 1882 the doubt as to the territory to be embraced by the operations of the survey was removed by the addition of the words "and to continue the preparation of a geological map of the United States." Under the directorship of Mr, Clarence King prominence was given to investigations of the mineral resources of the Rocky Mountain region in Colorado, Utah, and Nevada. A general division of mining geology was also organized, but, owing to the uncertainty of the area to be included under the term "national domain," its operations were limited to the States and Territories of the west. With the change of directorship in 1881 and the granting of authority in 1882 to complete a geological map of the United States, the policy of the survey was modified and its work was directed, under a very comprehensive plan, to the preparation of the required geologic map. This included the making of a topographic map of the entire United States as a base for the mapping of the areal geology. As adequate maps were not in existence, and areal geology without a good topographic base would be of little value, the topographic work was pushed forward; and in geology