324 ANNUAL OF SCIENTIFIC DISCOVERY. 



ON THE COMPOSITION OF SERPENTINE ROCKS AND ALLIED 



SPECIES. 



Some papers on this subject, read before the Nat. Hist. Soc. of Boston, by 

 Dr. A. A. Hayes, have thrown light on the chemical composition of the rocks 

 heretofore called serpentine: 



The research commenced on the ornamental mineral, which introduced 

 into the arts under the name of " Yerd Antique Marble," was found to be a 

 composite rock, containing an assemblage of minerals, known as talc, compact 

 asbestos, and actinolite, with occasionally fragments of silicious slate and 

 cour argillite, cemented by anhydrous carbonate of magnesia. This aggregate 

 receives a fine polish, and resists exposure to atmospheric agents as well as 

 the syenites, and is a remarkably beautiful and valuable mineral, largely 

 developed at Roxbury and Cavendish, in Vermont, the best quarries being 

 at Eoxbury. 



Finding the anhydrous carbonate of magnesia acting as a cement, to 

 possess an unlocked for resistance to the action of acids, and the rock to lose 

 its combined water on exposure to heat very slowly, it was at once apparent 

 that the analyses of serpentine rocks as published, might be incorrect in the 

 water determination. The experiments carefully conducted on specimens of 

 serpentine from the larger known localities, confirmed the conclusions in 

 regard to their composite character generally. The specimens yielded car- 

 bonic acid and magnesia as anhydrous constituents, while often the bulk of 

 the mineral was made up of talc, and compact asbestos in a more or less finely 

 divided state. The coloring matter was proved to be a silicate of proto-per- 

 oxide of iron, belonging to the green minerals aggregated, while the analyses 

 often showed the presence of nickel. In all cases the water, which was 

 variable in amount, belonged to the basis minerals, or those which the anhy- 

 drous carbonate of magnesia had cemented. The modern and the ancient 

 serpentines which have been celebrated, did not yield by the exact proximate 

 method of analysis any constituent which could be properly called a hydrous 

 silicate of magnesia. They all presented carbonic acid, magnesia, and talc, 

 while finely divided magnesia minerals, more or less hydrous, make up the 

 basis. It is well known, from the researches of Prof. Rogers and others, that 

 the magnesian minerals of the harder kinds, such as asbestos, yield to car- 

 bonic acid, dissolved in water, a portion of magnesia. The experiments of 

 Dr. Hayes harmonize with the conclusion, that the cementing material of 

 the serpentine rocks may be thus derived, and the research has an important 

 bearing in a geological view, as it proves that the serpentine rocks, so far as 

 they have been observed, are of aqueous or hot water origin, a heat above 

 that of 500 F. being inconsistent with their composition chemically. 



ON THE ORIGIN OF THE GAS CURRENTS IN SALIFEROUS 



DEPOSITS. 



At the German Association for the Promotion of Science, M. Schiibler, of 

 Stuttgard, presented some details of the facts ascertained in the mining 

 explorations in the Saliferous deposits, on effluvia of gas and subterraneous 



