THE UNITED STATES GEOLOGICAL SURVEY. 485 



In addition to the atove, areas amounting to abont one hun- 

 dred and six thousand square miles have been adopted from the 

 Powell, Wheeler, Hayden, and King surveys, and published on 

 the scale of 1 : 250,000. From this table it appears that during 

 the past twelve years the Geological Survey has mapped six hun- 

 dred and twenty-four thousand square miles, being more than one 

 fifth the area of the country, excluding Alaska. Of this, more 

 than two thirds is on the scale of 1 : 125,000, and nearly one sixth 

 on the scale of 1 : 62,500. 



Geologic Work. The geologic work is readily classified as 

 special i7ivestigations and areal mapping. 



The first branch of the geologic work, special investigations, 

 is illustrated by the study and report on The Tertiary History of 

 the Grand Canon District, by Captain C. E. Button ; Lake Bonne- 

 ville, by Mr. G. K. Gilbert; Geology and Mining Industry of 

 Leadville, Colorado, by Prof. S. F. Emmons ; The Palaeozoic 

 Fishes of North America, by Prof. J. S. Newberry ; and the 

 thorough investigation of the geologic phenomena of the Yellow- 

 stone National Park, by Mr. Arnold Hague. Twenty-four mono- 

 graphs and one hundred and sixteen bulletins have been pub- 

 lished by the survey as the results of such investigations. They 

 are frequently the basis of generalizations that must be obtained 

 before the areal geologic work can be successfully prosecuted ; 

 and the areal geologist is constantly making use of the data fur- 

 nished him by the specialist. Immense collections have been ac- 

 cumulated in the laboratories of the survey and in the National 

 Museum, which are the basis of correlations used almost con- 

 stantly in areal mapping and frequently in the solution of prob- 

 lems arising in connection with the study of economic questions 

 of a high order. The interrelation of the various branches of 

 geology are such that all must be kept up to a high standard, or 

 all will sooner or later deteriorate and thus affect the quality of 

 the output of results by the survey. 



Under the direction given, in 1882, to complete the geological 

 map of the United States, a comprehensive scheme of work was 

 outlined. A large corps of geologists soon began work on various 

 problems that arose in planning a system of mapping that would 

 serve for all phases of geology to be met with in the three million 

 square miles of the area of the United States. A large amount 

 of valuable detailed local work had been done by various State 

 surveys ; several of the Government surveys had made more or 

 less complete reconnaissances of large areas west of the Missis- 

 sippi River, and a few fairly accurate geologic maps were pub- 

 lished by them ; but the State and Government surveys had been 

 conducted each in its own way and with little regard to co-ordi- 

 nation with the work of the others. It was necessary to bind 



