. Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society. o a knife-edge, with spursflanked by steep talus slopes and precipitous Avails. High on the eastside the sediments lap against the steep liUcolith, dipping 51^ to theeast, and the limestone shows small faulting Avith western descending the east slope, beds from Cambrian to Minnekahta lime-stone (Permian) are crossed in a distance of one-half mile, and the transi-tion to low dips and horizontality is very sudden. The most stri
. Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society. o a knife-edge, with spursflanked by steep talus slopes and precipitous Avails. High on the eastside the sediments lap against the steep liUcolith, dipping 51^ to theeast, and the limestone shows small faulting Avith western descending the east slope, beds from Cambrian to Minnekahta lime-stone (Permian) are crossed in a distance of one-half mile, and the transi-tion to low dips and horizontality is very sudden. The most strikingrevet crags are seen on the south side of the mountain, where they formcrescentic ridges with bare limestone crests, separated from one anotherby V-shaped trenches that give passage to rills which regularly fork intotwo within the V along the porphvuy-Cambrian contact. Fragmentsof brown sandstone and Scolithus quartzite occur near the porphyry,and in a few hundred yards the geologic section from Carboniferous toPermian shoAvs a change in dip from 60° to 0° (fig. 93). This suddenchange of dip in consecutive outcrops of overlapping strata is charac-. Kio. 91.—Citadel Rock, looking northward toward Crow Peak. of the steeper (see fig. 92), and the in Avhichthe change takes place is sometimes actually less than the normal thick-ness of the beds irnol ved. The structure shoAvn aa-ouUI not permit uni-fonn cui-vature of all the strata OAor the dome. The only explanationfor such structure is that there has been rupture of the hard beds, withstretching, compression, and flow in the soft beds. The soft botisthick(>n in the concavities and thin on the arch. Crow Peak is encir-cled on the east, south, and Avest l)y Higgins and Crow creeks and theirtributaries; on the north a Hat upland slope of Minn(>l<ahta limestoneextends out to the Red YalloA, Avhcrc it abruptly bends doAvnward, sandstone forms a ridge to the northwest, Av
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