LAURENTIAN AND EARLY PALAEOZOIC. 19 



that such conditions may have been general or universal 

 in the primeval times we are here considering. 



If we ask to what extent the carbon extracted from 

 the atmosphere and stored up in the earth has been, 

 or is likely to be, useful to man, the answer must be 

 that it is not in a state to enable it to be used as min- 

 eral fuel. It has, however, important uses in the arts, 

 though at present the supply seems rather in excess of 

 the demand, and it may well be that there are uses of 

 graphite still undiscovered, and to which it will yet be 

 applied. 



Finally, it is deserving of notice that, if Laurentian 

 graphite indicates vegetable life, it indicates this in vast 

 profusion. That incalculable quantities of vegetable 

 matter have been oxidised and have disappeared we may 

 believe on the evidence of the vast beds of iron-ore ; and, 

 in regard to that preserved as graphite, it is certain that 

 every inch of that mineral must indicate many feet of 

 crude vegetable matter. 



It is remarkable that, in ascending from the Lauren- 

 tian, we do not at first appear to advance in evidences 

 of plant-life. The Huronian age, which succeeded the 

 Laurentian, seems to have been a disturbed and unquiet 

 time, and, except in certain bands of iron-ore and some 

 dark slates coloured with carbonaceous matter, we find in. 

 it no evidence of vegetation. In the Cambrian a great 

 subsidence of our continents began, which went on, 

 though with local intermissions and reversals, all through 

 the Siluro-Cambrian or Ordovician time. These times 

 were, for this reason, remarkable for the great abundance 

 and increase of marine animals rather than of land-plants. 

 Still, there are some traces of land vegetation, and we may 

 sketch first the facts of this kind which are known, and 

 then advert to some points relating to the earlier Algae, 

 or sea- weeds. 



An eminent Swedish geologist, Linnarsson, has de- 



