Reviews 



Prelimhiary Description of the Geology and Water Resources of the 



Southern half of the Black Hills and Adjoining Regions in South 



Dakota and Wyoming. By N. H. Darton. [Extract from 



the Twenty-first Annual Report of the U. S. Geol. Surv.^ 



1899-1900, Pt. IV, Hydrography; pp. 489-599; Plates 



LVIII-CXII ; Washington, 1901.] 



The topics discussed in this paper are topography, stratigraphic- 



geology, geologic structure, geologic history, water resources, minerals, 



soils, climate and timber. The Black Hills rise out of the Great 



Plains as a small group of forest covered mountains several thousand 



feet high. Their central area, composed of mountains and parks, is of 



crystalline schists and granites. Bordering the old rocks is a belt of 



limestone plateaus surrounded in turn by the Red Valley, a depression 



resulting from the etching out of a layer of softer rock — the Spearfish 



formation of Triassic age. Beyond the valley and concentric with it 



is the hogback range, due to a hard sandstone not weathered down. 



Still farther outward are the Plains. Careful descriptions of the litho- 



logic characters and the distribution of each formation follow ; in 



fact the paper is descriptive rather than theoretic, but does not fail to 



call attention to broad features and to make generalized statements. 



The oldest sediments are Cambrian. They are probably of later 

 Cambrian time and give one more item of evidence leading to the con- 

 clusion that Cambrian time was one of extensive submergence. Here 

 Cambrian sands were deposited along seashores and in estuaries with 

 gradual submergence and probable ultimate covering of the crystallines 

 with sediments of this age. The chief evidence is the presence of fine 

 grained deposits in the Upper Cambrian such as are not formed near 

 land. At present no Silurian or Devonian strata occur. The reason 

 is problematic. Either there was no deposition or else little deposition 

 and subsequent removal. Carboniferous time began with deep water 

 and marine conditions, and was consummated after the laying down 

 of 800-1000 feet of rock. Triassic and Jurassic are both present and 



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