NOTES IN RELATION TO THE ACCOMPANYING CONTOUR-MAP 

 OF THE UNITED STATES. 



Bv Hexhy Gaxxett, M. E. 



I have been eugaged for several years in collecting elevations in the 

 United States, particularly in that portion west of the Mississippi River. 

 In connection with this work, I have made a quite extensive study of 

 the geography, both horizontal and vertical, of the country, having had 

 access to nearly all sources of such information extant. 



By means of the numerous reconnaissances and surveys of different 

 parts of the West, there is scarcely any part of this vast area of which 

 the general features at least are not known. The necessity for further 

 reconnaissance, as such, no longer exists, while the need of actual sur- 

 veys, based on exact methods, increases year by year, as the work of 

 settlement goes on. In the accompanying map, I have sought to em- 

 body some of the results of my studies. It represents approximately 

 and as nearly as the information available at present will enable me to 

 do it, the locations of contour-curves over the country. 



The vertical distance between the curves is 1,000 feet. 



This map is published merely as a beginning in this direction, and 

 as much with a desire of gaining information by criticism as of imi^art- 

 ing knowledge on the subject. 



The map on which the curves were drawn, and of which this is a 

 photo-lithographic copy, is that used by the Census Bureau for their 

 atlas. It is not all that could be wished for the purpose, as it contains 

 many errors in drainage, geographical positions, &c., due to the fact 

 that the latest geographical work is not represented upon it. In gen- 

 eral, I have made the contours conform to the drainage ; but in a few 

 cases, where this would necessitate marked errors in the curves, the 

 course of the drainage has been neglected, and the contours have been 

 drawn as I know them to exist, as in the case of Preuss Lake, Utah, which 

 has lately "been proven to have no existence, and the mouth and lower 

 course of theEio Dolores in Eastern Utah, which have been sadly mis- 

 placed by map-makers since the time of Captain Gunnison. The scale 

 of the map is smaller than I should wish, and makes it impossible to 

 represent properly many features which could be brought out on a larger 

 map. 



Exact measurements of elevation above sea-level are in this country en- 

 tirely unknown, except near the coast. Ko leveling for scieutitic pur- 

 poses, on any considerable scale, has been done ; and the levels of rail- 

 road and canal lines, though at first they might seem to be all that is re- 

 quired, on examination are found to be as conflicting as possible. No 

 two lines give the same height for the terminus. The profiles of the 

 railroads, when compared, present a mass of contradictions almost be- 

 yond belief. The discrepancies, however, are due, not to the instru- 

 mental work, but to the office-work, the computations, the connection 

 of different sections, &C. The matter is greatly complicated by uncer- 

 tainty concerning the identity of datum-planes, especially when such 

 datum-planes are given as mean, high, or low water in lakes or rivers. 



