. 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. areespecially high, one of them rising 500 feet above the bed of the creek below. Viewed from the south, they bear, collectively, strong resemblance to a huge dike,but on ascending the highest of them, one is impressed with the almost plug-likecharacter of the mass. The Carboniferous limestone can be seen to the east, northand northwest, forming a wall about the uplift. On the west there seems to be anextension of the porphyry. On the s
. 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. areespecially high, one of them rising 500 feet above the bed of the creek below. Viewed from the south, they bear, collectively, strong resemblance to a huge dike,but on ascending the highest of them, one is impressed with the almost plug-likecharacter of the mass. The Carboniferous limestone can be seen to the east, northand northwest, forming a wall about the uplift. On the west there seems to be anextension of the porphyry. On the south great blocks of indurated sandstone occurand the Cambrian is extensively exposed in this direction. * * * In betweenthe lower porphyry hills exposures of Cambrian shale occur, as if in its intrusion therock had included a portion of that series above itself, and had ele^•ated this to thelevel of the surrounding limestone. [Compare Sheep Mountain, Dome Mountain,and ^^hitewood Canyon laccolith, tig. 91 and Pis. XX and XXI.] ^A contribution to the geology of the northern Black Hills, by J. D. Irving: Annals New YorkAcad. Vol. XII, , jAGGAR.] LACCOLITHS SUBORDINATE TO CEMENT KIDGE. 249 It will be seen from this description that the Needles are a subordi-nate laccolith like Ragged Top, flexing back the massive limestone onthe side remote from the greater Cement Ridge masses, and wereinjected probably in a highly viscous condition through the Cambrianbeds on the northern border of the larger southern laccolith. Ikying ashort distance west of Crow Peak, the Needles occupy a similar positionstructurally. The rock of the Needles is somewhat unusual—a diorite-porpyhry without mica, containing phenocrvsts of automorphic horn-blende, sanidine, and plagioclase in a groundmass of plagioclase,magnetite, and orthoclase. INYANKARA MOUXTAIX. Inyankara Mountain was described by Winchell ^ more accuratelythan l)y Newton. The mountain rises on the outer side of the RedVall
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