THE PROGRESS OF LIFE 53 



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 occur- 

 rence of graphite and limestone 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 pro- 

 bable that both graphite and limestone may be due to 

 the decomposition 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 limestones 

 are of organic origin, for no organism could have 

 existed under such conditions. 1 



HURONIAN LIFE 



No undoubted traces of life have been found in the 

 Huronian of America ; but it is probable that the sup- 

 posed Radiolarians and sponges, discovered by Dr C. 

 Barrois, in Brittany, should be placed in it. 



The animal origin of Dr Cayeux's specimens has 

 been doubted by some palaeontologists ; but, if we may 

 rely on the accuracy of the published figures which 

 has not been challenged they certainly appear to be 



1 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 disputed by Dr H. Rauff, of Bonn. 



