550 REVIEWS 



Less-pure residual clays, derived from rocks of various kinds and ages, are found 

 at many points in the state, and are used in places for brick manufacture. 

 Siebenthal, C. E. The Silver Creek Hydraulic Limestone of Southeastern 

 Indiana. Twenty-fifth Ann. Rept. Indiana Dept. Geology and Natural 

 Resources Pp. 331-389, PI. 14, colored geologic map, 1901. 



Divided into three sections relating respectively to the stratigraphy, topography 

 and economic geology of the Silver Creek limestones. 



A historical resume of opinions in regard to the stratigraphy of southeastern Indi- 

 ana is followed by descriptions of local distribution and structure. The Devonian and 

 sub-Carboniferous formations occurring in this area, with their New York and Missis- 

 sippian (paleontologic) equivalents, are : 



„ , „ , ., ( Knobstone ' Kinderhook. 



Sub-Carboniferous j Rockford limestone Choteau. 



f New Albany black shale Genesee. 



I Sellersburg limestone Hamilton. 



Devonian \ Silver Creek hydraulic limestone Hamilton. 



j Jeffersonville limestone Corniferous. 



[_ Pendleton sandstone Schoharie. 



The topography is briefly mentioned. Pleistocene terraces are described and 

 mapped, and a possible preglacial channel of the Ohio River is pointed out. 



The Silver Creek hydraulic limestone is massive, very fine grained and usually 

 fossiliferous. In color it varies from light to dark or bluish-drab, weathering buff. 

 In composition it varies between the following limits : Calcium carbonate 52 per 

 cent, to 62 per cent.; magnesium carbonate 16 per cent, to 35 per cent.; silica 9.5 per 

 cent, to 18.5 per cent.; ferric oxide 1.4 per cent, to 2.0 per cent.; alumina 2 to 5 per 

 cent. The cement rock is obtained by quarrying or mining, according to the situa- 

 tion ; blasted out by dynamite and sledged to proper size (6"-i2") for the kilns. The 

 latter are continuous up-draft kilns, and require about seventy-two hours for calcina- 

 tion. The burned rock is sent through crushers, " re-grinders," and rock-emery mills. 

 During 1900, thirteen plants, working 1 16 kilns, were in operation, the total product 

 being 2,512,000 barrels. 



