THE TOPOGRAPHIC SURVKY OF MICHIGAN. 161 



THE TOPOGRAPHIC SURVEY OP THE UNITED STATES. 



At the begiiiuiug of the work of the United States Geological Survey, 

 in 1879, there was no map available of the region to be studied, which 

 would serve as a basis for the geologic map ordered by Congress. To 

 meet this difficulty, a topographic division of the survey was promptly 

 organized, and slowly drilled until it became fully as efficient as any 

 other similar corps in the world. During the past twenty-three years, 

 the arduous task of making a contour topographic map of the United 

 States has been carried steadily forward, and greater and greater excel- 

 lence in the finished maps secured, as a result of increasing experience 

 and more and more exacting demands. The maps produced during the 

 past decade are worthy of critical comparison with the best maps of 

 like character on the same scale, and produced at similar cost, made any- 

 where in the world. 



The plan adopted by the United States Geological Survey in mapping 

 our country, is to divide it into quadrangles, representing what is termed 

 one square degree. That is, the standard sheets include one degree of 

 latitude and one of longitude. The area shown on each sheet varies in 

 accord with its geographic position, but in general embraces about 900 

 square miles. These maps are drawn to scale of about two miles to one 

 linear inch, or TrsVoiT of nature, and relief is shown by contour lines, 

 with intervals ranging from 100 to 20 feet, according to the roughness 

 of the land. When circumstances render a larger scale desirable, how- 

 ever, the quadrangle is made to include one-quarter of a square degree, 

 and the scale is enlarged to one mile to one inch, with contour intervals 

 of 20 feet, or less. Special maps are also made on still larger scale for 

 mining, municipal and other purposes. On these maps the lakes, streams, 

 etc., or the hydrography, are represented in blue; the contour lines in 

 brown, and the cities, roads, houses, etc., or what is termed "culture," 

 in black ; the lettering is also in black. 



Contour topographic maps of the character briefly described above, 

 have been made by the United States Geological Survey when the demand 

 for them as base maps for geologic work was greatest. The maps now 

 available embrace a portion of every state and territory in the Union, and 

 although to a great extent the published sheets are disconnected and in- 

 dependent, each one has its" allotted place in the contemplated map. Up 

 to the present time about one-third of the area of the United States has 

 been surveyed, and for the completion of the task at the rate it has been 

 progressing during the past decade, at least fifty years will be required. 



CO-OPERATION BETWEEN THE FEDERAL AND STATE SURVEYS. 



The topographic work of the United States Geological Survey, as stated 

 above, is primarily to furnish a base for a geologic map, and has been 

 carried on where the demand for such maps, particularly of mining re- 

 gions, is most urgent. For this reason the work has been distributed 

 without reference to state boundaries. Several states, however, recog- 

 nizing the value of the topographic maps the Federal survey is making, 

 and cognizant of the fact, also, that when once topographic maps are 

 available, detailed geologic and forestry surveys, conducted by the gen- 

 eral government usually follow, have been anxious that topographic maps 

 should be made of their entire areas. With this aim in view, several 

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