GEOLOGY. 39 



kind will be suggested by the action of rivers, by coasts and hollows 

 which are being- silted up, without the necessity of seismic disturbance, 

 or, comparatively speaking, much difference of level. Still it appears 

 strange if this were the case that the original order should not be more 

 frequently met with in connexion with these deposits ; and, further, if the 

 prevalent arrangement were not the original one, it would be expected 

 that in such great natural salt-pans as the grand Runn of Kutch, thin 

 layers of gypsum would be found underlying the incrustation of salt, 

 no instance of which has come to notice. 



The effects of pressure and heat combined have been appealed to 

 (Phillips) in order to account for possible conditions under which the 

 deposition as found could have taken place ; and these are indicated 

 among other causes (such as chemical and molecular change, percola- 

 tion, and magnetic currents) for metamorphism of strata as deposited 

 into rocks like these, reasoning based on these suggestions being 

 thought likely to lead to a solution of the problem (Page) . Besides solar 

 evaporation, gaseous emanations of solfataras and mineral springs are 

 hinted at by Lyell as capable of connexion with these deposits ; but all 

 authorities seem united in the opinion that we require further knowledge 

 of the chemical changes in seas where volcanic agency is in progress, 

 of the ancient hydrography of salt regions, the chemistry and physi- 

 cal geography of the ocean, before "results apparently beyond the 

 production of any known operations in nature" can be satisfactorily 

 accounted for. 



With reference to heat as one of the conditions among those just 

 mentioned, it should be noticed that the presence of small quantities of 

 petroleum or other hydrocarbon in the Kohat salt, if coeval, may be 

 evidence against any temperature high enough to have driven this off. 



In conformity with the apparently received solar evaporation theory, 

 the salt or sea-water may have occupied a large evaporating basin over 

 much of the bottom of which it had laid down a deposit of gypsum. 

 The proportion of the latter in sea-water is greatly smaller than that of 



( L43 ) 



