Water Supply and Irrigation Papers of the United States Geological Survey . are shown on the geologic map(PI. I). To the southwest there are scattered areas at a number ofpoints between Edgemont and Pringle, notably on the Minnelusasandstone west of Argyle, in the Red Valley north and west of Minne-kahta, and on the Dakota sandstone not far north of of Oelrichs there is a narrow basin which has been preservedin a syncline extending toward the Big Badlands. The deposits of the White River group exhibit considerable diver-sity of composition. The principal material is a porous, cr
Water Supply and Irrigation Papers of the United States Geological Survey . are shown on the geologic map(PI. I). To the southwest there are scattered areas at a number ofpoints between Edgemont and Pringle, notably on the Minnelusasandstone west of Argyle, in the Red Valley north and west of Minne-kahta, and on the Dakota sandstone not far north of of Oelrichs there is a narrow basin which has been preservedin a syncline extending toward the Big Badlands. The deposits of the White River group exhibit considerable diver-sity of composition. The principal material is a porous, crumblingclay, pale flesh color when dry, but light brown when damp. Someportions of it are pale green when dry and olive when wet. Much ofit is fullers earth, and differs from ordinary clay in being much lessplastic. In the lower beds of the group it merges into sand on theone hand and into clay on the other. At many localities it is asso-ciated with or gives place to coarse materials occupying channels orbroad sheets. In the vicinity of Hermosa the principal material is. GEOLOGY OF THE BLACK HILLS REGION. 25 coarse sandstone and conglomerate, mainly of dark-brown color,which mantles extensive plateaus. On the high level ridge north ofSpring Creek there are coarse conglomerates, which extend entirelyacross the hogback range. About Fairburn and to the west thereare long channels filled with conglomerate consisting of limestonepebbles and a calcareous matrix. These extend up several of thedepressions through the hogback range, either displacing the fullersearth deposits or being intercalated among them. The limestonepebbles appear to have been derived from Tertiary limestones, forthey do not represent any of the Mesozoic or Paleozoic rocks of thehills. On the higher lands of the Red Valley, between Hermosa andRockerville, there is an extensive deposit of nearly pure limestone,giving rise to a high plateau of considerable extent. The total thick-ness of the rock is about 30 feet at
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