REVIEWS 733 



distinguishable because an abrupt change in the character of the sedi- 

 ments and some erosion occur at the top of the former. Cretaceous 

 sediments have accumulated to the thickness of about 6000 feet and 

 consist largely of shales with some sandstone and a little limestone. 

 Tertiary rocks represented by the White River formation are mostly of 

 clay; fuller's earth, sand, limestone, and grits occur. Still later 

 deposits are classed under earlier and later Pleistocene beds. 



The structure of the region is that of an elongated low dome with 

 anticlinal wrinkles or spurs running off from the central area. The 

 maximum uplift was north of Harney's Peak and amounted to 9000 

 feet. 



One of the most admirable features of this paper is the abundance 

 of real geographic material embodied in it. The region described is 

 one of submaturely dissected, domed mountains in which all the sedi- 

 ments have been removed from the central portion leaving subdued 

 hills and broad parks of crystalline rocks. The concentric arrange- 

 ment of the different formations is due to the uplift and to the pro- 

 cesses of erosion which though similar for all strata, have been much 

 more effective in reducing some than others. Soft layers are found 

 etched out, hard layers standing up, but each and every one has its 

 peculiar forms. Thus geography follows stratigraphy. 



Attempts by the author, more or less successful, to reconstruct the 

 geography of the locality at different periods and to follow it through 

 its phases, are persistently made, and they yield an interesting element 

 in the work. In this connection there is a contour map showing the 

 present relief of the upper surface of the Dakota sandstone over a part 

 of the area. This kind of work forms a very desirable feature. 



The considerable eastward dip away from the Black Hills, where 

 most of the formations outcrop, together with other necessary features, 

 gives good artesian conditions to this region. Many wells reaching 

 the Dakota and Lakota sandstones flow with good water. The scanty 

 rainfall on the plains eastward renders these wells very useful. Many 

 streams diminish or cease by sinkage when they cross the sands. 

 Along Cheyenne and Fall rivers there is some opportunity for irriga- 

 tion — good bottom lands and reservoir space, with fair water supply. 



Soils are mostly residuary from underlying rocks. Overplaced soils 

 and sand dunes are found in places. "Sedentary soils" may be criti- 

 cised. No soil is sedentary in the sense that it does not move. " Soil in 

 place" or preferably "residual soil" more adequately carries the 



