CHAPTER XVI. 



ORIGIN OF THE ORE. 



Solvents possibly due to reduction by carbon. I have shoWll that ciniiabaV and 801116 



of the accompanying minerals are dissolved as sulphosalts. It is now desir- 

 able to consider how the alkaline snlphides essential to these solntions are 

 formed. The alkalis found in thermal springs are easily explained, inasmuch 

 as feldspathic rocks afford an inexhaustible supply of sodium and potassium. 

 The source to which sulphur must be attributed is less clear. Many geo- 

 logical chemists, among them Bischof, maintain that sulphides and free 

 sulpluir are ultimately referable to the reduction of soluble sulphides by 

 organic matter. That sulphides and sulphur are frequently produced in 

 this way is entirely beyond question, for the reduction has been effected 

 experimentally and has been observed many times under natural and arti- 

 ficial conditions. Gypsum, for example, in contact with water and carbon, 

 3^ields hydrogen sulphide and acid calcium carbonate, or calcite and car- 

 bonic anhydride. If salts also be present which ma^' be decomposed by 

 sulphydric acid, sulphides will be formed. 



Soluble sulphates exist in the greatest abundance in nature, being 

 found in nearly all spring water and forming some of the principal constitu- 

 ents of sea water. There can also be no doubt that a very large part, if 

 not the whole, of the water flowing from thermal springs and ejected by 

 volcanoes is of superficial origin and must have carried soluble sulphates 

 with it to the depths at which its temperature was raised to a maximum. 

 Organic matter is also held in solution or mechanical suspension in many 



438 



