Reviews — E. Daubr^e — Subterranean Waters. 567 



having a concretionary structure, either metalliferous or sterile. 

 " This is not so much an immediate product of the rocks themselves 

 as a gentle and prolonged deposit proceeding, some from gaseous 

 emanations, others and these the most numerous from powerful 

 mineral and thermal springs, whose first origin must be attributed to 

 the appearance of the eruptive masses, and whose circulation is 

 effected by the aid of the cracks or fractures of the ground " (Daubree, 

 op. cit. p. 143). There can be no better proof of the intimate con- 

 nection between mineralizing waters and metallic veins than is 

 afforded by the wonderful phenomena of the Steamboat Springs in 

 Nevada, of which a notice was given in the Quarterly Journal of the 

 Geological Society by William P. Blake as long ago as 1864. 

 Since then the whole of this Comstock region has been the subject 

 of numerous memoirs. According to Mr. Phillips (Ore Deposits, 

 p. 532), these rocks have been carefully assayed, with the results 

 that the neighbouring diabase contains a notable amount of the 

 precious metals, of which the larger proportion is contained in the 

 augite ; that the decomposed diabase contains about one-half as much 

 of these metals as the comparatively fresh rock ; and that the relative 

 quantities of gold and silver, both in the fresh and decomposed 

 diabase, correspond fairly well with the known composition of the 

 Comstock bullion. There does not seem any reason why these facts 

 should exclusively favour the theory of lateral secretion, but tbey 

 serve to confirm the notion as to the eruptive rocks being, in this 

 case, the primary source of the metallic wealth of the country, 

 which has been extracted and concentrated, as it were, for the benefit 

 of miners by the aid of heated and mineralized waters, in such 

 fissures as the Great Comstock Lode, where the process may still, to 

 a certain extent, be in operation. 



The replacement of limestone by ironstone, and the phenomena 

 connected with iron deposits generally, are also fully treated by 

 the author, who reproduces some of Mr. Kendall's sections showing 

 the mode of occurrence of heematite in Cumberland and North 

 Lancashire. 



Next comes the question of the change in rock-masses on a large 

 scale — and firstly, as to the mineralization of fossils, and the for-' 

 mation of nodules (rognons), etc. There can be no difficulty in 

 believing that water, in conjunction with dissolved salts and gases, 

 has replaced shell substance by a more or less pure mineral calcite, 

 and that sometimes the replacing substance has been silica, carbonate 

 of iron, or other mineral, even specular iron, as some bivalves he 

 mentions in the Lias. The numerous silicified woods also find a 

 place here. The flints of the Chalk he treats as concretionary 

 bodies, and he gives a telling figure of orbicular silex as developed 

 in the shell of a Grijplicea. The chemical alteration of silicated 

 rocks is next dealt with ; and here Mons. Daubree observes with 

 regard to the kaolinization of felspar, that this has not in all cases 

 been effected by surface agents ; he suggests aqueous and other 

 emanations in connection with the deposits of tin-ore. 



A considerable number of pages are devoted to the great question 



