SALINE GROUP. 79 



dolomitic layers are apparent. The curvature mig-lit either result from 

 general disturbance of the whole strata, or from partial motion iu the 

 saline series only, and would go to prove a certain flexibility even in 

 the crystalline salt rockj which must have crystallised in horizontal 

 planes originally. Superincumbent pressure is of enormous force in the 

 mines, the strongest stone masonry, even in arches, being crushed out 

 of form, and where large 40 feet pillars of salt are left to support 

 the roof, this vertical pressure causes huge flakes of the mineral to 

 separate. 



At the ends of ^'drifts" also the pressure causes large pieces to flake 

 off the vertical surfaces left unsupported by working out. 



The whole mass of the salt-mines hill is subject to percolation of 

 small quantities of rain water, which would eventually cause movement 

 and slippage under the pressure alluded to. 



The compact solidity of the salt may be inferred from the fact that 

 sounds travelling through it are audible at distances of 110 to 130 feet 

 (as proved by Dr. Warth^'s measurement) . The miners often, in approach- 

 ing drifts, signal to each other by blows of a sledge on the face into 

 which they are cutting. 



Sulphate of magnesium (Epsom salts) is mentioned in small quanti- 

 ties in some of the analyses (given by Dr. Warth) 

 Associated salts, 



made from waste-salt ; its existence is doubtful, 



except to a very trifling extent in the mass of this rock-salt, but it 

 impregnates the hallar and thin layers between the salt-beds. It also 

 efiloresces from the surfaces of the red marl in old workings. 



Dr. Warth has also found in the mines a white mineral composed of 

 gypsum, chloride of sodium, and sulphate of magnesium, besides very 

 beautiful, long, curving, fibrous, spun-glass-like crystallizations of salt 



( 79 ) 



