Ml". T. S. Hunt on some Points in Chemical Geology. 149 



still forming, alkaline carbonates which play a most important part 

 in the chemistry of the seas. 



§ V. The study of the chemistry of mineral waters, in connexion 

 with that of sedimentary rocks, leads the author to believe that the 

 result of processes continually going on in nature is to divide the 

 silico-argillaceous rocks into two great classes ; the one characterized 

 by an excess of silica, by the predominance of potash, and by the 

 small amounts of lime, magnesia, and soda, and represented by the 

 granites and trachytes ; while in the other class silica and potash 

 are less abundant, and soda, lime, and magnesia prevail, giving rise 

 (by metamorphism) to triclinic felspars and pyroxenes. The me- 

 tamorphism and displacement of sediments may thus, he observed, 

 enable us to explain the origin of the different varieties of plutonic 

 rocks without calling to our aid the ejections of a central fire. (See 

 § III.) 



§ VI. The most ancient sediments, like those of modern times, 

 were doubtless composed of sands, clays, and limestones ; but, on 

 the principles laid down in §§ IV. and V., the author shows that the 

 chemical composition of the sediments in different geologic periods 

 must have been gradually changing. Illustrating his views by the 

 condition of the Canadian rocks, Mr. Hunt observes that, on the 

 large scale, in the more recent crystalline or metamorphic rocks, we 

 find a less extensive development of soda-felspar, while orthoclase 

 and mica, chlorite and epidote, and silicates of alumina, like chias- 

 tolite, kyanite, and staurotide (which contain but little or no alkali, 

 and are rare in the older rocks), become abundant. The decomposi- 

 tion, too, of the rocks is more slow now, because soda-silicates are 

 less abundant, and because the proportion of carbonic acid in the 

 air (an efficient agent in these changes) has been diminished by 

 the formation of limestones and coal. 



§ VII. The author accepts the views of Babbage and Herschel as 

 to the internal heat of the earth rising through the stratified depo- 

 sits, on account of the superficial accumulation of sediments, meta- 

 morphosing the rocks submitted to its action, causing earthquakes 

 and volcanic irruptions by the evolution of gases and vapours from 

 chemical reactions, and giving rise to disturbances of equilibrium 

 over wide areas of elevation and subsidence. 



§ VIII. Mr. Hunt observes that the structure of mountain-chains, 

 both those due to the uprise of metamorphosed rocks through ter- 

 tiary and secondary de])osits, and those formed of older masses of 

 sediment, contorted and altered, bears out the principles of § VII. 



January 19. — Prof. J. Phillips, President, in the Chair. 



The following communications were read : — 



1 . On the Gold-field of Ballaarat, Victoria. By H. Resales, Esq. 

 Communicated by W. W. Smyth, Esq., Sec. G.S. 



Mr. llosales described tlie position of the quartz-lodes (the matrix 

 of the gold) in the schists of the hill-ranges, from whence originate 

 the numerous auriferous gullies, forming eventually several channels 



