Federal Surveys by civil Bureaus. 103 



various scales from 1 : 10,000 to 1 : 80,000. Contour lines at verti- 

 cal intervals of 10 or 20 feet are located on the planetable sheets. 

 The small scale charts are published in hachures, those on the 

 larger scales commonly in contours. 



Geological Survey. — The United States Geological survey is the 

 ■ only organization which has ever undertaken to map the United 

 States under a comprehensive and well defined plan, and it has 

 surveyed a greater area than any other organization. It was 

 formed in 1879 upon the discontinuance of the three rival western 

 surveys, namely, the Hayden, Wheeler and Powell surveys. At 

 first it was restricted in its operations to the public domain, but 

 was soon authorized by laAV to include the entire United States. 

 The work of topographic surveying on a large scale, with a view 

 to mapping the entire country, was commenced in 1882 and has 

 been prosecuted actively since that time. 



The work, wherever practicable, is controlled by triangula- 

 tion, which, though not of geodetic refinement, is suitable for the 

 control of the maps upon the adopted scales. Where it is not 

 practicable to carry on triangulation for control, traverses are run 

 for that purpose with instruments of considerable power and with 

 all possible precaution to prevent the accumulation of sensible 

 error. 



Aside from the primary control, location is effected by graphic 

 methods. The planetable is used for secondary triangulation 

 and for traversing. Heights are measured with the spirit level, 

 by vertical angles, and by aneroid. The maps are now pub- 

 lished on two scales, one of 1 : 62,500, or about one mile to an 

 inch, the other of 1 : 125,000, or about two miles to an inch. 

 Considerable work has been executed on the scale of 1 : 250,000, 

 but that scale has been abandoned. Relief is expressed by con- 

 tours, the intervals ranging from 5 feet Up to 200, depending upon 

 the scale and upon the degree of relief of the country. 



The Geological survey has worked in cooperation with four 

 states, namely, Massachusetts, Rhode Island, Connecticut and 

 New Jersey, and has completed the surveys of these states. It 

 has also surveyed large areas in New York, Pennsylvania, Mary- 

 land, Virginia and West Virginia, the southern Appalachian 

 region, Louisiana, Texas, Arkansas, Illinois, Iowa, Wisconsin, 

 Missouri, Kansas, and the western states and territories gen- 

 erally. Altogether an area of 550,000 square miles has been 

 surveyed. The maps are engraved on copper. Three plates 



