. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. AMERICAN GEOLOGY—SURVEYS UNDER HAYDEN. 601. liase line «,«»> ft. Fi». 1. Section across Northern Gr 7 miles j£\* In describing the Sierra La Sal south of the Gunnison in the report for 1875, Peale compared them in structure with the Elk Mountains— that is, as of eruptive origin. "By this," he wrote, "] mean that the sedimentary strata have been lifted up by eruptive rock which has broken through them in some places, and in
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. AMERICAN GEOLOGY—SURVEYS UNDER HAYDEN. 601. liase line «,«»> ft. Fi». 1. Section across Northern Gr 7 miles j£\* In describing the Sierra La Sal south of the Gunnison in the report for 1875, Peale compared them in structure with the Elk Mountains— that is, as of eruptive origin. "By this," he wrote, "] mean that the sedimentary strata have been lifted up by eruptive rock which has broken through them in some places, and in others is seen only as the result of subsequent erosion.'1 As illustrative of this, he gave the figure reproduced here. (Fig. 106.) The idea thus advanced seems to have been contagious, for in the same report Holmes described the Sierra El Late as formed of a number of distinct bodies of trachytic rock that had reached their present horizon through closely associated vents, frequently bending up e the sedimentary rocks at a high angle around the borders, the upturned strata including the lower part of the Middle Cretaceous shales and portions of the Dakota sandstone. His obser- vations tended to show, to quote his own words, ""that there had been a sort of absorption, so to speak, of the shales, and that at least half of the space through which the trachyte is distributed is occupied by the crushed and metamorphosed fragments of shale. As a consequence the height of the arch—such as may once have existed—would not equal the height of the trachytic mass, as only the higher layers of shale extend entirely over it. His idea regarding the formation of this mountain can be best understood by reference to tig. 107, copied from Plate l»i in the report for ; (See further on p. 622.) «The views regarding this: method of mountain formation were subsequently summed up by Peale in an article, On a Peculiar Type of Eruptive Mountains in Colorado, which wa
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