Hypsometric sketch of the United States [Accompanying Text]. Side: 224
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224
To untangle this mass is an enormous labor, and one perplexing in the
extreme. Many have undertaken it, and have given it up in despair. In
1874, Mr. J. T. Gardner, then connected with this Survey, undertook a
part of this labor, and succeeded in carrying it through with a consid-
erable degree of success. His problem was, to obtain the true eleva-
tion of Denver, Colo., which serves as a hypsometric base for our work
in Colorado. To this end, he connected a number of lines from the
Atlantic and Gulf coasts, rooted out nearly, all the errors, and finally
obtained results for the heights of several of the most important rail-
road-centers, which, from their close agreement, show a strong, proba-
bility of being correct. Should these results, on the application of
further tests, prove trustworthy, they will form a frame-work, by use of
which the problem will be simplified very much.
Elevations measured by barometer are liable to large errors, unless
the work is done under the very best circumstances. The most potent
causes of error are too great distance, horizontal and vertical, from
the barometric base. In the earlier days of exploration in the West,
it was impossible to obtain even tolerable conditions for the execution
of hypsometric work. Hence, naturally, the earlier measurements of
elevations in the West are found to presents wide range of error, some
being changed scarcely any by later and more reliable measurements,
others being several hundreds of feet—indeed, in some cases reaching
a thousand feet—from the truth.
In constructing these curves, though I have made use of the many
thousands of elevations in my possession, I have borne in mind that ele-
vations of isolated points merely, without a knowledge of the surround-
ing topography, are of little use. Indeed, in many cases they are worse
than useless, as they may tend to mislead.
The mean heights of mountain-ranges have been expressed as nearly
as possible. They will, no doubt, be subject to much criticism, as many
of them are based on insufficient information, and my estimate of the
mean heights of others, based on the heights of a few peaks, may not be
correct.
In the canons of the Colorado and Green Rivers, I have thought best,
owing to the small scale of the map, to run the contours into a single
line.
The sources of information consulted and made use of in this work
are almost numberless. I will enumerate the principal ones. For a
knowledge of the Appalachian system and the country adjacent, I am
indebted mainly to the article by Professor Guyot on the Appalachian
system, published in vol. xxxi (1861) of Silliman's Journal; also, in
various State geological and geographical reports, there is much ma-
terial of value concerning the Eastern States. Information concerning
the valley of the Mississippi is scattered far and wide, and to specify
authorities would fill a volume.. Reports of State and General Gov-
ernment surveys and profiles of railroads have supplied the greater part
of this information.
On the slope of the great plains, between longitudes 96° and 104°,
the contours are controlled largely by the plotted heights. These
heights have been collated from, first, the profiles of the several rail-
roads which cross the plains, the Northern Pacific, Union Pacific, Bur-
lington and Missouri River, Kansas Pacific, Atlantic and Pacific, Ar-
kansas Valley, and others of less importance; and, second, from the
profiles of the routes of the numerous expeditions which have crossed
the plains in various directions.
The Llano Estacado and the western part of Texas are known mainly
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Gannett, Henry, 1846-1914. Hypsometric sketch of the United States [Accompanying Text]., map, 1876; Washington, D.C.. (https://texashistory.unt.edu/ark:/67531/metapth310694/m1/4/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting University of Texas at Arlington Library.