REPORT OF THE SECRETARY. 67 



United States, thereby giving the Survey authority to extend its opera- 

 tions over the entire country in so far as necessary to effect that pur- 

 pose. Inasmuch as the preparation of a geologic map requires a cor- 

 rect topographic map as its basis, it became necessary to adopt a scale 

 for a general map of the United States, and also a method of graphic 

 representation. The experience of the various geologic surveys carried 

 on by the General Government and by the several States has shown 

 that the smallest scale that can ordinarily be used on a map for general 

 geologic purposes is 4 miles to the inch, and that vertical relief is best 

 indicated by contours with intervals of 25 feet or 200 feet, according aa 

 the country represented is plain or rugged in its topographic features- 

 Certain districts in which the geology is complex may require elaborate 

 maps on larger scales, but for the general map the scale of 4 miles to> 

 the inch has been adopted as best suited for the purpose of geologic 

 representation. 



It is proposed to publish this general map in atlas sheets, each to 

 include one degree of longitude by one of latitude. 



To accomplish this topographic work in the shortest possible time 

 and with the greatest economy, it was decided to take advantage of all 

 work previously done, whether by the General Government, by the 

 several States, by counties, townships, or by industrial corporations 

 and individuals. In order to compile and adjust the material obtained! 

 from these various sources, a topographic division was organized, under 

 the charge of Mr. Henry Gannett, who, in addition to the work of com- 

 pilation and adjustment above referred to, began field operations, car- 

 ried on to a limited extent in 1882, but extended and systematized in 

 1883. 



Topographic Work. 



The plans for the topographic field work for the season of 1883 con- 

 templated a large increase of work in the Southern Appalachian region,, 

 the commencement of work in Massachusetts, the further prosecution 

 of work in New Mexico and Arizona, in Northern California, and the 

 commencement of a detailed map of the Yellowstone National Park, It 

 was further proposed to extend the map of the Elk Mountains in Colo- 

 rado, which was made by the survey under Dr. F. V. Hayden in 1874, 

 besides numerous detailed maps in different sections of the country. 

 Field work in the Arizona and New Mexico district, known as tbe "Win- 

 gate division," was commenced in the latter part of May,under the direc- 

 tion of Prof. A. H. Thompson. The division was organized first witli 

 one party for carrying on triangulation and two for topographic work, 

 which organization was continued until the 1st of July, when another 

 topographic party was added. The character of the country, which 

 consists essentially of rolling plateaus commanded by buttes of no 

 great height, was such as to permit of very rapid topographic work. 

 The weather also was favorable during the entire season, and the result 

 was that this division covered a very large area, estimated at 22,000 



