CHEMICAL AND DYNAMICAL GEOLOGY. 79 



tact with metallic salts which are precipitated as sulphides. It is thought that all 

 sulphides owe their origin, directly or indirectly, to the reducing power of or- 

 ganic matter. Water also takes up from decaying vegetation much soluble earthy 

 matter. Carbon di-oxide gives it the property of dissolving limestone and 

 dolomite which it then holds in solution in the form of bi-carbonates. The por- 

 osity of rocks I ermits the water to gradually sink beneath the surface, so that 

 portions of it come in contact with rock and minerals far beneath. The follow- 

 ing figures, showing the amount of water by volume and by weight that loo parts 

 of different rocks will hold, are taken from a table pre ared by Hunt : 



Volume. Weight. 



Sandstone — Potsdam, hard and white 1.39 0.50 



Sandstone — Potsdam, with lingula 9.35 3.96 



Sandstone — Medina, red argillaceous . , 10.06 4- 04 



Limestone — Trenton, gray crystalline 1.70 0.65 



Limestone — Trenton, black, com, acted 0-30 o.ii 



Dolomite — Niagara, gray, crystalline , . 5.27 2.08 



Dolomite — Chazy, argillaceous 13-55 5-55 



Dolomite , calciferous 7.22 2.27 



Limestone — Tertiary (Caen, France.) 29.49 15-85 



Feldspathic rocks, especially soda feldspars, are disintegrated by these 

 waters charged with carbon di-oxide, yielding sodium carbonate and clay. The 

 economy of nature is here nicely illustrated by the fact that the soil takes from the 

 water the salts of potassium and ammonium, which are so necessary for plant 

 life, while it gives sodium in return. Thus the waters that are continually entering 

 the ocean, seas and lakes, contain almost no potassium, but large amounts of 

 sodium in the form of carbonate. In early geologic times, when the air contained 

 much more carbon di-oxide than now, and the earth much more albite and 

 oligoclase — soda feldspars — these actions were probably much more rapid. The 

 first reaction between the sodium carbonate and the salts of the sea water would 

 result in converting the calcium chloride into calcium carbonate, (limestone), 

 sodium chloride, (common salt), being formed at the same time. This, perhaps, 

 was the origin of nearly all the calcium carbonate the ocean water ever contained. 

 In lakes and inland seas where it would be possible to thus decompose all the 

 calcium chloride, the next action would be the conversion of magnesium chloride 

 into magnesium carbonate, with the further formation of sodium chloride. 

 Much of the calcium would be in the form of bi-carbonate, which would react 

 on any magnesium sulphate present, making calcium sulphate, or gypsum, and 

 magnesium carbonate. In these inland seas, where evaporation was continually 

 going on, the gypsum would soon be deposited. Should the concentration be 

 continued, magnesium carbonate would be thrown down along with great quan- 

 tities of limestone. If such inland seas could occasionally receive an influx of 

 salt water, as many such seas do at the present day, the precipitations would be 

 repeated. If the concentrations should ever be carried far enough salt would 



