HOW THE WATERS OP THE OCEAN BECAME SALT. 53 



sucli as oligoclase and albite, aud the decomposition of 

 these components wonld hasten that of the less sohible 

 varieties, 



15) It seems not improbable from certain considerations 

 connected with the organic structures of the ancient world, 

 that carbon-dioxide was more abundant in the atmosphere 

 of Palseozoic times than at present. The enormous quantity 

 of carbon which must have been extracted from the air 

 during the Carboniferous period in order to the formation of 

 the beds of coal at intervals all over the w^orld, seems to 

 favour this view ; and if this be so, then we may suppose 

 that previous to tlie Carboniferous period, the air Avas highly 

 charged with carbon-dioxide, and the process of decompo- 

 sition on the land surface was carried on with even greater 

 rapidity than at the present day ; but even had this not been 

 the case, it only requires a sufficiently long period in order 

 to bring about the chemical reactions necessary to the 

 salinification of the oceanic waters. 



20 We are now approaching the conclusion of our enquiry. 

 From the examples of closed lakes we can determine the 

 process of salinification with the utmost certainty. Through- 

 out greater or shorter periods, these lakes have been 

 receiving the waters of rivers bringing down, both 

 mechanically suspended sediments and chemically dissolved 

 salts, silicates and carbonates. The sediments are precipi- 

 tated over the bottom of the lakes, and the water bemg 

 carried off into the atmosphere in the form of vapour as 

 fast as it enters, leaves behind the dissolved ingredients. 

 These necessarily augment in quantity, and ultimately the 

 waters of the lakes become saturated with salts and carbon- 

 ates, which are then deposited. 



21 Now the ocean is a closed lake of enormous magnitude. 

 Throughout all geological time it has been receiving con- 

 tinual supplies from rivers bringing down not only sediment, 

 but salts and carbonates, together with free silica, in solution. 

 The sediment is deposited over the ocean floor, and generally 

 not far from the lands, while the dissolved ingredients are 

 carried by the currents into all parts. Meanwhile the ocean 

 surface is constantly giving off, particularly over the 

 equatorial regions, enormous quantities of vapour which 

 are carried into the higher regions of the atmosphere, and 

 are precipitated in the form of rain and snow over the lands. 

 Part of course falls on the sea again, but the greater 

 quantity falls on the laud surfaces, aud is returned to the 



