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of the origin of rock salt : — volcanic agency in conjunction ■« ith 

 earthquake action ; marine explosion, or overflow of sea-water 

 and subsequent evaporation ; or gradual recession of sea-water and 

 deposition of salt as it receded. The generally received opinion 

 is that it is the result of volcanic force. There are strong facts 

 in favour of that theory. Gigantic mountains, composed of rock 

 salt, stand solitary in districts where there are no traces of saline 

 matter for hundreds of miles : thus one near Cordova is 500ft. 

 high and three miles in circumference. Isolated masses are 

 found in Lahore, Peru and other countries. On the south of the 

 Dead Sea there is a mountain of rock salt extending five miles 

 with a height from 200 to 400ft., but here the whole district is 

 charged with salt. Lastly, there is the Indian salt range. These 

 masses might have been elevated through the crust of the earth 

 by some ancient volcanic force. Another fact which favours its 

 seismological or volcanic origin is that rock salt is often found 

 in close relation with gypsum, or sulphate of lime, known to be 

 invariably the production of some subterranean action. 



The objection to this theory is the total absence of 

 organic remains in rock salt, while gypsum is very rich in remains 

 of organic matter. But rock-salt is not always found in 

 juxtaposition to gypsum. It is not confined to any particular 

 group of strata. The salt mines of Galicia belong to the 

 Tertiary, those of New York to the Silurian system, and in this 

 country the Trias is the chief repository of salt. It is also 

 present in the Lias. These facts indicate that it is not the 

 result of regular geologic action, but probably due to volcanic 

 agency. It has been suggested that an igneous origin of rock-salt 

 and gypsum is not at all unlikely, and that the consolidation of 

 both rocks was caused by intense heat, but there is the difficulty 

 of the diff'erence of the two rocks as to organic remains. 



It was found by the Challenger that volcanic detritus is 

 almost uniformly scattered over the floor of the ocean, and in 

 such quantities that all the volcanoes, active and exhausted, 

 would not suffice to eject material in such an enormous amount 

 as to spread it over so vast a surface. There must be other sub- 

 marine vents to account for such a distribution. As to the theory 

 of marine explosion as an origin of rock-salt, it must not be for- 

 gotten that marine explosion and volcanic action are generally 

 simultaneous. 



The bottom of the ocean is in a continual state of change. 

 There is a presumed subterranean communication between the 

 North Sea and the Caspian, and other such communications be- 

 tween distant seas and inland lakes. What is more probable than 

 that under-currents of water, dense with salt, pass into subter- 

 ranean caverns, deposit their salt, and flow back to the ocean ; 

 that this process, going on for centuries, forms beds of salt, which 



