. 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. ma>s. The northern border of the Vanocker jiorphyry mass betweenAlkali Creek on the east and the eastern fork of Park Creek on thewest, including the basin at the head of Deadman Gulch, is a dilferentrock from the rest of the mass, ])eing a fine-grained rhyolite, whilethe greater ]iortion is a coarse syenite-poi-phyiy. The contact between. Fig. 84.—Southwist bunUT of Vaiiookcr laccolith. Elk Creek, .showiiiK k these t

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. 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. ma>s. The northern border of the Vanocker jiorphyry mass betweenAlkali Creek on the east and the eastern fork of Park Creek on thewest, including the basin at the head of Deadman Gulch, is a dilferentrock from the rest of the mass, ])eing a fine-grained rhyolite, whilethe greater ]iortion is a coarse syenite-poi-phyiy. The contact between. Fig. 84.—Southwist bunUT of Vaiiookcr laccolith. Elk Creek, .showiiiK k these two rocks follows roughl} the divide at the head of DeadmanGulch and the northern slopes of the valleys of the two creeks men-tioned, but a definite contact was nowhere found; possibly the finer-grained northeastern portion was more rapidly cooled against the sed-imentary cover, and is a differentiated facies of the larger mass.

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