GYPSUM, ROCK SALT. 289 



occurs, is in that tertiary series found about Paris, 

 and elsewhere ; alternating, there, with argillaceous 

 and calcareous marl, while lying immediately above 

 the limestone, and forming distinct hillocks. There 

 are th/ee strata, separated by the same intervening 

 materials ; the lowermost containing no extraneous 

 fossils, while the middle one is remarkable for the 

 remains of fishes. The uppermost, sometimes exceed- 

 ing eighty feet in thickness, and lying immediately 

 below the soil, is still more interesting, as including 

 the bones of various land animals, formerly noticed, 

 and amply described by Cuvier. 



Rock Salt. 



Although Salt cannot, more than Gypsum, be classed 

 among the rocks, it forms a necessary part of the 

 present enquiries. 



It is very widely distributed throughout the earth, 

 as has appeared in the account of the red marl ; and 

 its existence rna'y often be surmised from the pre- 

 sence of salt springs, lakes, and saline efflorescences, 

 .in countries where its masses are not visible. It 

 abounds in England, having been long wrought in 

 Cheshire ; while the salt springs of Northumberland, 

 Durham, and Leicestershire, indicate its probable 

 existence in places which the operations of the miner 

 have not yet reached. In Spain, an extensive reposi- 

 tory of it occurs between Caparoso and the Ebro ; as 

 does a bed of five feet in thickness, accompanied by 

 gypsum and limestone, at Valtierra. At Cardona, it 

 is extensively wrought, and is also found in La Mancha, 

 near Burgos, and in other places which I need not 

 enumerate. Rock salt, or salt springs which appear 

 to arise from repositories of it, occur in many parts of 

 France ; as at Salies, to the south of Thoulouse, at 



VOL. n. u 



