. 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. ubse(juent valleys having courses concentric to the dome tend to fol-low along the strike of the Paleozoic and Mesozoic beds. The mostconspicuous of these valleys is the well-known Red Vallev, whichforms a continuous depression around the Black Hills uplift. 1)RAINA<;k of tkkrv pkak district. Four streams drain the Teny Peak eruptive center, flowing east,northeast, and north; these are Elk, Bear Butte, Whitcwood, andSpearfish creeks.
. 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. ubse(juent valleys having courses concentric to the dome tend to fol-low along the strike of the Paleozoic and Mesozoic beds. The mostconspicuous of these valleys is the well-known Red Vallev, whichforms a continuous depression around the Black Hills uplift. 1)RAINA<;k of tkkrv pkak district. Four streams drain the Teny Peak eruptive center, flowing east,northeast, and north; these are Elk, Bear Butte, Whitcwood, andSpearfish creeks. The drainage system of each of these has erodedaway strata which capped igneous intrusives; and the porphyries,by reason of their more resistant quality, usually form prominenteminences above the general level. The westernmost of the streams mentioned, Spearfish Creek, formsfor 20 miles an impressive canyon in the limestone plateau, from whichthe stream emerges into the Red Valley at Spearfish. For a portion ofits course this stream, which is to-day one of the most powerful in theHills, flows along the contact of the Algonkian schists with the basal174. TOPOGRAPHY. 175 beds of the Cambrian; above the mouth of Annie Creek the streamleaves the last outcrop of schist, and from here to the mouth of Robi-son Gulch, under Spearfish Peak, flows on Cambrian beds, cuttinginto porphyry masses at Annie, Squaw, and Rubicon gulches; thenentering the zone of dipping Paleozoics, it progressively cuts its wayacross Silurian, Carboniferous, and Permian beds before emerging onthe Triassic lowland of the Red Valley. (See Pis. XVIII and XIX.) Whitewood and Bear Butte crocks, which flow to the northeast,traverse a more varied topography before they emerge from the take their rise among Cambrian strata and porphyries, and theirheadwater branches have assisted in carving out the northern portionof the exposed Algonkian core of the Black Hills uplift. Through por-tions of their co
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