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<br /> <br />GEOLOGY. <br />any, in_ There is nat a ESood.geolo~ical survey of ..the District, The country <br />principal rock is ,.Trachyte and~porph;~ry of the Tertiary period. <br />ce at _ ,. . <br />Treas., . <br />ver, Colo. <br />ny. <br />s 1892, <br />iin- <br />mine <br />