ANCIENT LIFE ON THE EARTH 17 



they are entirely the result of hydrothermal action 

 on lime-bearing silicates ; but it does not necessarily 

 follow that they must be organic. Also, we can 

 hardly suppose the large quantities of graphite found 

 in these limestones to be organically derived ; for, if 

 this had been the case, it must have come from 

 marine plants no others being in existence and, 

 as we have no knowledge of any mineral carbon- 

 compounds having thus originated in large quantity 

 in any other period, we should have to suppose that 

 seaweeds were either more abundant or more capable 

 of being preserved in the Archaean era than at any 

 later time. The occurrence of graphite and lime- 

 stone together suggests a common origin for both ; 

 and, as we know that metallic carbides occur, not 

 only in meteorites, but also in the terrestrial iron of 

 Ovifak in Greenland, it seems probable that both 

 graphite and limestone may be due to the decompo- 

 sition of calcium carbides by hot water. At any 

 rate, if the officers of the Canadian survey are right 

 in their ideas as to the genesis of the Grenville 

 series, we cannot possibly suppose that the lime- 

 stones are of organic origin, for no organism could 

 have existed under such conditions. 6 



Huronian Life. No undoubted traces of life have 

 been found in the Huronian of America ; but it is 

 probable that the supposed Eadiolarians and sponges, 



6 I have not seen Dr. Mathew's paper on Archseozoon and 

 Sponges from the Upper Laurentian. near St. John, New 

 Brunswick, in the Bulletin of the Nat. Hist. Society of 

 New Brunswick ; but their organic nature has been dis- 

 puted by Dr. H. Rauff, of Bonn. 



