Bibliographical Notices. 455 



of the position, characters, and origin of the " Eefractory Siliceous 

 Ores" is full of information as to discovery, exploitation, extent, 

 characters, and the value of the several bodies of ore in the Bald 

 Mountain area (with its subordinate districts), also in the Garden, 

 Lead, Yellow Creek, and Squaw Creek areas. 



The component minerals of these bodies of ore are quartz, 

 chalcedonic silica, pyrite, arsenpyrite, barite, fluorite, gypsum, 

 stibuite, and uranium-mica; but they exhibit cousiderable variations, 

 due to local alterations and rearrangements of constituents. The 

 methods of mining and treatment of the ores are referred to at 

 page IGO. 



The production of these Cambrian Siliceous ores in the Xorth 

 Black Hills, in 1897, has been reported as amounting to $2.1 64.287.58 

 (page 117). The ore-bodies (or "shoots") occur as more or less 

 banded masses, with a " channel-like " form, nearly parallel to the 

 bedding-planes of the strata in which they are found, and are thick 

 in the centre with vertical extensions, and thin at the periphery. 

 Their origin is probably due to the passage of mineral waters along 

 the planes of bedding, and in very numerous cross-fractures, giving 

 rise also to extensive mineralization of the neighbouring ("country") 

 rocks. The text-figures at pages 126, 132, and 157, as well as 

 plates xi. to xvii., are especially illustrative of these " Refractory 

 Siliceous ores." The reason for the name here given to them is 

 explained at page 111. 



loiva Geological Survey. — Yol. XIY. Annual Report., 1903, with 



Accompanying Papers. Samuel Calvijt, A.M., Ph.D., State 



Geologist. T. Savage, Assistant State Geologist. With 664 pages, 



38 plates, and 132 text-figures. Des Moines, Iowa Geological 



Survey, 1904. 



The mineral products of Iowa are generalized at pages 9-26, with 



their localities according to Counties, and with the relative value of 



the coal, clay, stone, gypsum, lead, zinc, and limestone. Of these 



the clays are the most important ; and a full account of the clay 



industries in the State constitutes the main subject of this useful 



volume. 



Bages 29-348 treat of the " Technology of Clay." This abundant 

 hydrous silicate of alumina originates in the decomposition of the 

 felspar in granite and other rocks ; and, being distributed by rain, 

 river, and sea, is ultimately collected by nature in various modes 

 and conditions, known to geologists generally, and practically to 

 agriculturalists, civil engineers, and makers of pottery and other 

 ceramic ware. For them this chapter proceeds to treat in detail of 

 the origin and natural })istory of clay, how it is got, how prepared, 

 and of its economic uses. The physical properties and consequent 

 characters of clay are described ; and chemical analyses, both of the 

 raw and the burnt material, are given. Thus the relative fineness of 

 grain in the fresh clay (p. 116) is very important in judging the 

 probable results in proposed manufacture of any kind of brick, tile, 



