. Contributions to the geography of the United States, 1923-1924. Geology; Mines and mineral resources. 118 COjSTTRIBUTIONS to geography op united states^ 1923-1934. of the rocks, as illustrated in Figure 15. In some places the over- hanging material will fall, as illustrated at h and c, or slump, as at d and e. If such a slumping extends to the surface, the condition illustrated in Plate XXIX, A, may result. At the locality shown a limestone block has slumped because of the removal of gypsum from beneath it. The winds and floods bear surface material into the openings. The coarser matter lodg
. Contributions to the geography of the United States, 1923-1924. Geology; Mines and mineral resources. 118 COjSTTRIBUTIONS to geography op united states^ 1923-1934. of the rocks, as illustrated in Figure 15. In some places the over- hanging material will fall, as illustrated at h and c, or slump, as at d and e. If such a slumping extends to the surface, the condition illustrated in Plate XXIX, A, may result. At the locality shown a limestone block has slumped because of the removal of gypsum from beneath it. The winds and floods bear surface material into the openings. The coarser matter lodges near the entrance; the finer is distributed more widely by the underground streams. A fall from the roof of a cavern may choke a passageway, as illustrated at d, Figure 15, or the cavern may gradually fill until it is completely sealed up, as at g^ and made water-tight so that new openings are sought, as at / and «, which in turn filled in time, producing. Figure 15.—Sketch, section illustrating the formation of solution, cavernsi in strata con- taining gypsum, and rock salt. The caverns are formed in the gjrpsum and rock salt, and connecting channels are cut through the limestone and other strata. At the bot- tom of opening a is some of the material "o which fell from the roof ; at c material whlchi fell within, the ; at cb and e massesi of hard rock which, slumped when support was removed from one side; f a. small choked opening; at g an old sealed opening. the condition illustrated in Figure 16, where undisturbed strata end abruptly against detrital matter, as at a, or disturbed strata lie in an unnatural position (h) surrounded by fragmental material (c) with caverns (d) filled and sealed. In places where the soluble material has been removed more rap- idly than at neighboring localities, or where the filling has not kept pace with the removal of soluble matter, the collapse of the rocks near the surface has formed basins, such as Alkali Flat an
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