The Origin of Rock- Salt. 41 



minerals, much might be said. Two points, however, may- 

 be referred to — rather in the form of suggestive questions 

 than as direct statements. (1) Is there not some connec- 

 tion between the formation of chlorides in metalliferous 

 deposits, and the presence, now or formerly, of concentrated 

 solutions of chloride of sodium ? I am thinking specially of 

 Atacamite; but the same suggestion recalls the chlorides of 

 silver, and also the curious association of gold with regions of 

 aridity. In the case of arid conditions, chlorine seems to 

 take much the same part in bringing about changes near the 

 surface in the case of metalliferous deposits as carbonic acid 

 does under humid conditions. (2) Chloride of sodium is one 

 of the substances given off by some active volcanoes. Is 

 this due to the surplus from the sea- water, which I hold to be 

 one of the prime factors in the generation of all eruptive 

 rocks ? If more sea- water finds its way downward to the 

 volcanic foci than is needed for furnishing the alkalies 

 required for the making of the volcanic rocks, one can 

 readily understand how, in the general process of concentra- 

 tion which the sea- water undergoes by plutonic causes, some 

 of the salt may not be required, and may reach the surface 

 either as a gas, or as a residual deposit from some other vapour. 

 The following works (amongst others) may be consulted 

 upon various points connected with Salt. A fuller list will 

 be found in the footnotes to chap, xviii. vol. i. of Bischofs 

 " Chemical Geology." 



Maxwell Lyte, "Salt," Ency. Brit., 9th ed.; Ditmar, ''Sea- 

 Water," ihid. 



Reclus, La Terre, vol. ii. 



BiscHOF, Chemical Geology, vol. i. chap, xviii. 



Justus Roth, " River- Water, Sea-Water, and Rock-Salt," Cont. 

 Eevietv, August 1880. 



Lothian Bell, Salt Deposits of Middleshoro. 



J. J. Manley, Salt and other Condiments, International Health 

 Exhibition, 1884. 



" Salt and Gypsum Industries of the United States," Bulletin 

 New York State Museum, vol. iii. No. 11 (1893). 



Wagner's Chemical Technologic, '* Water," International Health 

 Exhibition, 1884. 



