FOSSIL FOOD 285 



sank towards the centre, while the lighter, now represented 

 by the ocean and the atmosphere, floated in a gaseous con- 

 dition on the outside. But the great envelope of vapour 

 thus produced did not consist merely of the constituents of 

 air and water ; many other gases and vapours mingled with 

 them, as they still do to a far less extent in our existing 

 atmosphere. By-and-by, as the cooling and condensing pro- 

 cess continued, the water settled down from the condition of 

 steam into one of a liquid at a dull red heat. As it condensed, 

 it carried down with it a great many other substances, held in 

 solution, whose component elements had previously existed 

 in the primitive gaseous atmosphere. Thus the early ocean 

 which covered the whole earth was in all probability not 

 only very salt, but also quite thick with other mineral mat- 

 ters close up to the point of saturation. It was full of lime, 

 and raw flint, and sulphates, and many other miscellaneous 

 bodies. Moreover, it was not only just as salt as at the pre- 

 sent day, but even a great deal salter. For from that time 

 to this evaporation has constantly been going on in certain 

 shallow isolated areas, laying down great beds of gypsum 

 and then of salt, which still remain in the solid condition, 

 while the water has, of course, been correspondingly puri- 

 fied. The same thing has likewise happened in a slightly 

 different way with the lime and flint, which have been 

 separated from the water chiefly by living animals, and 

 afterwards deposited on the bottom of the ocean in immense 

 layers as limestone, chalk, sandstone, and clay. 



Thus it turns out that in the end all our sources of 

 salt-supply are alike ultimately derived from the briny 

 ocean. Whether we dig it out as solid rock-salt from the 

 open quarries of the Punjaub, or pump it up from brine- 

 wells sunk into the triassic rocks of Cheshire, or evaporate 

 it direct in the salt-pans of England and the shallow salines 

 of the Mediterranean shore, it is still at bottom essentially 



