48o THE POPULAR SCIENCE MONTHLY. 



relating to problems directly affecting tlie study of rocks or min- 

 erals, 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 engrav- 

 ing 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 lime- 

 stones, 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 survey- 

 ing. The second and third floors are occupied by the geologists 

 of the survey, and the first floor by the administrative ofiices, 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 prepa- 

 ration of a geological map of the United States." Under the di- 

 rectorship of Mr, Clarence King prominence was given to inves- 

 tigations 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 opera- 

 tions 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, un- 

 der 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 spe- 



