Page:Popular Science Monthly Volume 58.djvu/523

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By Professor WILLIAM H. HOBBS,


IN no country of the world does the government distribute to its people with so lavish a hand as in our own the published results of scientific investigation. One example among many that might be given is furnished by the reports of the United States Geological Survey, which for abundance of material, for scientific value and for beauty of illustration are not approached by the geological publications of any European state. Of the many who see the beautifully colored geological maps which accompany these magnificent reports, or the only less elaborate and expensive maps prepared by certain of the individual States, doubtless few have the faintest notion of the studies on which they are based.

No comprehensive study can be made of the geology of any region until some sort of geographical map of the region makes it possible to represent the exposed rock masses in approximately their true positions relative to one another. If the geology be other than of the very simplest character—and this will generally be true of mountainous regions—it is not only necessary to fix the geographical positions of rock masses, but their elevations as well. In other words, the map must not only be a plan, but special elevations must be represented, known as geological sections. The most satisfactory representation—and this will be essential for all difficult areas—will be one which shows not only special elevations, but the topographic relief of every point in the area. A proper preparation for detailed geological work in a difficult area involves, therefore, the making of a relief or topographic map based on correct triangulation, and of a scale and an accuracy of delineation of relief forms commensurate with the complexity of the geological structure. For large areas of the eastern United States such maps have been prepared by the United States Government, sometimes in cooperation with the State governments, and these maps maybe obtained in the form of beautifully engraved atlas sheets by any one and at merely nominal prices. On these maps are shown in black the railroads, highways, houses, etc. (the culture); in blue, the lakes, streams, swampy areas, etc. (the hydrography); and in brown, the lines of approximately equal altitude (the topography).

With such a map the field geologist can begin intelligently his geological work. This work will consist first of all in the collecting of his