ANCIENT LIFE ON THE EAETH 27 



tained, in addition to its present salts, mineral 

 hydro-carbons which would slowly oxidise and supply 

 the organisms with food, without the necessity of 

 decomposing carbon-dioxide. Now Professor H. 

 Moissan has shown that much, if not all, of the 

 carbon of the earth existed at first as metallic car- 

 bides, many of which are decomposed by water at 

 ordinary temperatures, and yield hydro-carbons and 

 hydrogen. Most of the hydro-carbons thus obtained 

 are gaseous (acetylene and marsh-gas) ; but in some 

 cases both liquid and solid hydro-carbons are formed 

 abundantly. 9 The gases would be partly taken up by 

 the water, while the liquid and solid forms would 

 float on the surface, and, if converted into carbo- 

 hydrates, may have served as food for the first 

 organisms. It is, therefore, quite possible to suppose 

 that protoplasm capable of secreting chlorophyll was 

 a later development, when the supply of mineral 

 hydro-carbons were getting exhausted; and, conse- 

 quently, the first organisms may have been animals. 



ORDOVICIAN AND SILURIAN LIFE 



I now pass on to glance at the life of the Ordo- 

 vician and Silurian periods. The Ordovician was 

 ushered in by the appearance of the highest sub- 

 kingdom of animals, the vertebrata, represented by 

 minute teeth, called conodonts, from the green sands 

 at the base of the Ordovician, near St. Petersburg. 



9 Proceedings of the Poyal Society of London, vol. lx., 

 p. 156. 



