Water Supply and Irrigation Papers of the United States Geological Survey . Note: Figures denote depths of borings MAP OF A PORTION 01 if without + signquartzitewasmet withatthatdepth Showing d Ail depth areas estimated averagesThequartzitesurface has many local irregularities by: I 200 - 300 WATER-SUPPLY PAPER N° 34 PL. IV. STERN SOUTH DAKOTAj to bed rock )D 1899 J LIU US BIEN B CO. LITH N. 500-600 600-700 S00-900 900-1000 1000-110(1 roDD.] GENERAL GEOLOGY. 15 COLORADO FORMATION. This includes two series of deposits, which were first separated byDr. F. Y. Hayden. The lower series, composed mo
Water Supply and Irrigation Papers of the United States Geological Survey . Note: Figures denote depths of borings MAP OF A PORTION 01 if without + signquartzitewasmet withatthatdepth Showing d Ail depth areas estimated averagesThequartzitesurface has many local irregularities by: I 200 - 300 WATER-SUPPLY PAPER N° 34 PL. IV. STERN SOUTH DAKOTAj to bed rock )D 1899 J LIU US BIEN B CO. LITH N. 500-600 600-700 S00-900 900-1000 1000-110(1 roDD.] GENERAL GEOLOGY. 15 COLORADO FORMATION. This includes two series of deposits, which were first separated byDr. F. Y. Hayden. The lower series, composed mostly of shale andclay, was named Benton, from its great development near Fort Benton,Montana, and the upper series, composed largely of chalkstone, wascalled Niobrara. These two subdivisions, though usually differing con-siderably in lithologic character, are often grouped together becauseof the similarity of the fossils which appear in them. Moreover, theline between them is not easily established, because in many places thechalk grades into the clay and shale; and even when fairly pure,enough protoxide of iron is present to give it a bluish tint resemblingthe shale. It has been found very difficult to separate them in thisarea by means of the reports of well-borers. One well-borer will saythat within a given region
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