542 



THE WONDERS OF GEOLOGY. Lect.V. 



acid.* In Tuscany, boracic acid is obtained from jets of 

 vapour which force their way through secondary rocks in 

 contact with serpentine, f 



The connexion between volcanic action and the for- 

 mation of gypsum, seems also pointed out by the fact, that, 

 in North America, where volcanic rocks are not associated 

 with the coal measures, there are no beds of gypsum : but 

 in Nova Scotia, where igneous rocks are interpolated 

 beneath the coal, there are extensive gypseous deposits.^ 

 Mr. Lyell, after a careful review of the phenomena exhi- 

 bited by these gypsiferous strata, expresses his conviction, 

 that the production of gypsum in the carboniferous sea 

 was intimately connected with volcanic action, whether in 

 the form of stufas or heated vapours, or of hot mineral 

 springs, or some other effects of sub-marine igneous erup- 

 tions. 



I may, also, remark, that the variegated appearance of 

 the marls, — red, pink, blue, yellow, dun, &c. — of the Trias, 

 seems to have been produced by the chemical effects of 

 vapours or fluids charged with sulphuric or chloric acid ; at 

 least the same change is induced on the tertiary marls of 

 the Lipari Isles, by the gaseous emanations and vapours of 

 the fumaroles and hot springs. 



5. The Cheltenham Waters. — In certain localities 

 where the marls of the Trias are covered by other beds, 

 and the saline springs force their way to the surface through 

 the superincumbent deposits, chemical changes take place 

 in these solutions of chloride of sodium, which thus acquire 



* Mr. Playfair informed Dr. Buckland, that, during an eruption of 

 Vesuvius, sulphuret of copper was ejected : and Mr. Fox states that 

 sulphuret of copper may have been deposited from solution in boiling 

 water. 



f See a highly interesting Memoir on the Geology of Borne part.- of 

 Tuscany, by W.J. Hamilton, Esq. M.P. GeoL Journal, vol.i. p. '274. 



J See Geological Journal, vol. iii. p. 257. 



