540 T HE WONDERS OF GEOLOGY. Lect. V. 



so largely and uniformly present, seems to indicate a com- 

 mon origin; both occur abundantly as volcanic products. 

 In a more advanced state of chemical science, this fact 

 may probably tend to the elucidation of the question under 

 consideration. 



The gypsum associated with rock-salt, is considered by 

 several eminent observers to be anhydrous, that is, entirely 

 free from water, before exposed to moisture. The great 

 beds of gypsum that occur with rock-salt at Bex, in Swit- 

 zerland, were found by M. Carpentier to be anhydrous 

 when laid open to the atmosphere. Hence Mr. Bakewell 

 suggests that the consolidation of the salt and gypsum, must 

 have been effected in such cases by heat, for there is no 

 conceivable mode of aqueous deposition that could form 

 anhydrous gypsum.* The red colour of the salt and 

 marls is occasioned by oxide of iron, which may have been 

 derived from decomposed trap rocks. 



That many of the deposits of salt may have originated 

 simply from the evaporation of sea-water pent up in 

 lagoons, lakes, or inland seas, is a generally received, and 

 not improbable supposition; but the absence of marine 

 organisms, of any kind, has been regarded as a formidable 

 objection to this hypothesis, f Another difficulty presents 

 itself in the enormous thickness of many of the beds of 

 salt ; which, if considered as the solid residuum of sea water, 

 must have required a body of fluid inconceivably great ; 

 unless we suppose the seas of those ancient periods to have 



* I would refer to Mr. Bakewell's Introduction to Geology, (5th edit, 

 p. 289,) for a luminous review of this problem, and a full account of 

 the most important deposits of salt. 



f It cannot however be with certainty determined, whether the 

 absence or paucity of fossils in a deposit is owing to an actual reduc- 

 tion of the amount of life in the seas of a given area, or to the mineral 

 character of the strata not having been favourable to the preservation 

 of organic remains. 



