CHAPTER IV. 



THE ORIGIN OF PLANT LIFE ON THE LAND. 



IF the graphite of the Laurentian rocks was derived from 

 vegetable matter, the further question arises, Was this vege- 

 tation of the land, or of the sea ? and something may be said on 

 both sides of this question. If there were land plants in the 

 Laurentian period, they must have grown either on rocks older 

 than the Laurentian itself, or on such portions of the beds of 

 the latter as had been raised out of the sea, forming perhaps 

 swampy flats of newly-made soil. But we know no rocks older 

 than the Laurentian, and there is no positive evidence that 

 any of the beds of that formation were other than marine. 

 Still it is not impossible that some of the beds which are now 

 graphitic gneisses may originally have been similar to the 

 bituminous shales, coals, or underclays of the coal formation. 

 The graphite occurring in veins, if of vegetable origin, must 

 have been derived from liquid bitumen oozing into fissures ; 

 and veins of this kind occur in later formations, both in marine 

 and freshwater beds. The only positive argument which has 

 been adduced in favour of the existence of abundant land 

 plants in the Laurentian is that of Dr. Sterry Hunt, derived 

 from the great beds of iron ore, which it is difficult to account 

 for chemically except on the hypothesis of the decay in the air 

 of great quantities of vegetable matter. The question must 

 remain in doubt till some one is fortunate enough to find 



