104 Henry Gannett — Mother Maps of the United States. 



are required, the culture, drainage and relief being printed in 

 different colors. 



Lake Survey. — The shores of the Great lakes and of the St Law- 

 rence river have been mapped, together with a narrow strip of 

 topography, by the organization knoAvn as the United States 

 Lake survey, which was under the control of the Engineer corps 

 of the United States army. Besides mapping the shores of the 

 lakes, this organization carried a belt of triangulation from the 

 head of lake Michigan to that of lake Erie across the southern 

 end of the peninsula of Michigan, and another strip of triangula- 

 tion through eastern Illinois to the neighborhood of Vincennes, 

 Indiana, and located by astronomic means a large number of 

 points in the lower peninsula of Michigan. All these determi- 

 nations of positions were connected directly with section corners 

 of the United States Land survey, to be hereafter described. 



The work of this organization was of a high order of excellence, 

 comparable in most respects to that of the United States Coast 

 and Geodetic survey. 



Engineer Surveys. — In connection with river improvements, the 

 United States Engineer corps has made surveys of many navi- 

 gable rivers. In many cases these are merely local surveys 

 covering trifling areas, but in the cases of the lower Mississippi 

 and the Missouri river excellent maps, controlled by triangula- 

 tion, have been produced. 



Army Explorations. — The Avestern part of the United States 

 has, ever since its acquisition, been a favorite field for explora- 

 tion and survey. For a long time the War department monopo- 

 lized this field. The explorations began with the famous expe- 

 dition of Lewis and Clarke in the early years of the century, 

 followed by those of Long, Pike and Fremont. Then, in the 

 early fifties, came that remarkable series of explorations known 

 as the Pacific railroad surveys. These were followed by numerous 

 other army expeditions, some of which are of comparatively 

 recent date. Altogether a large number of military parties have 

 traversed the Cordilleran region and each of these expeditions 

 has furnished more or less geographic information. 



Their methods of survey were, in nearly all cases, similar : A 

 traverse survey of the route was made, using the compass for 

 directions. Distances Avere measured by the 'revolutions of a 

 Avheel or by estimates based upon the time of travel. Points off 

 the line Avere intersected upon and thus located roughly Avith refer- 



