216 THE DAWN OF LIFE. 



largely supplied witli this very soluble salt^ instead of 

 the chloride of sodium^ or common salt, which now 

 prevails in the sea-water. 



Where in such a world would life be introduced ? 

 on the land or in the waters ? All scientific proba- 

 bility would say in the latter. The ocean is now 

 vastly more populous than the land. The waters 

 alone afibrd the conditions necessary at once for the 

 most minute and the grandest organisms_, at once for 

 the simplest and for others of the most complex cha- 

 racter. Especially do they afford the best conditions 

 for those animals which subsist in complex communi- 

 ties, and which aggregate large quantities of mineral 

 matter in their skeletons. So true is this that up to 

 the present time all the species of Protozoa and of the 

 animals most nearly allied to them are aquatic. Even 

 in the waters, however, plant life, though possibly in 

 very simple forms, must precede the animal. 



Let humble plants, then, be introduced in the waters, 

 and they would at once begin to use the solar light for 

 the purpose of decomposing carbonic acid, and forming 

 carbon compounds which had not before existed, and 

 which independently of vegetable life would never have 

 existed. At the same time lime and other mineral 

 substances present in the sea- water would be fixed in 

 the tissues of these plants, either in a minute state 

 of division, as little grains or Coccoliths, or in more 

 solid masses like those of the Corallines and Nulli- 

 pores. In this way a beginning of limestone forma- 

 tion might be made, and quantities of carbonaceous 



