1853.] Report on the Geological Structure of the Salt Range. 243 



Minerals. 



The only two minerals of importance which the red marl yields 

 are rock salt and gypsum. These we shall notice in detail. 



Bock Salt. 



This valuable mineral, the origin of which is so veiled in obscurity, 

 occurs in the marl apparently in a bed from 150 to 200 feet thick, 

 towards its upper surface, but wherever salt occurs, masses of it of 

 all sizes, which have been detached from the original bed, are found 

 scattered through the marl at various depths. 



Three varieties of salt occur, the red, the white and the trans- 

 parent or glass salt. The former is obtained in greatest quantity, 

 and being tougher and more difficult to reduce to powder than the 

 other two varieties, stands transportation better, and is consequently 

 in greatest demand among the salt merchants. 



The mineral in all its varieties is a nearly pure chloride of so- 

 dium, the only foreign soluble ingredient it contains being a trace 

 of sulphate of lime. Except when the salt is mixed with marl, it 

 contains no chloride of magnesium, an impurity which generally 

 occurs in rock salt, and the absence of which in that of the Salt 

 Range renders it but slightly deliquescent. The colour of the red 

 salt is not, as might be supposed, derived from a salt of iron or 

 manganese, but is probably of an organic nature. 



The salt has every appearance of having been formed by crystal- 

 lization from a brine solution, in which much marl as mud has at 

 times been mechanically suspended. At the lower and upper limits 

 of the bed, where the deposition of the salt has commenced and 

 ended, it is much mixed with marl, but in its interior this merely 

 forms thin partings in the pure salt, which mark its stratification. 

 As the salt presents more of a crystalline aspect in the interior of 

 the bed, than at either its upper or under surface, we are inclined 

 to think that it has been there formed during a very slow evapora- 

 tion of the brine solution, which from the absence of mud, must 

 have been in a state of great quiesence. The salt is every where 

 solid, and never presents cavities lined with crystals of salt, which we 

 would expect to find had it been a sublimed product. 



The salt bed bears evidence of having been exposed to violent 

 disturbing agency, as it can never be traced for any distance in the 



