LAURENTIAN AND EARLY PALAEOZOIC. 9 



manner great beds of iron-ore exist in the Laurentian ; 

 but in later formations the determining cause of the 

 accumulation of such beds is the partial deoxidation and 

 solution of the peroxide of iron by the agency of organic 

 matter. Besides this, certain forms known as Eozoon 

 Canadense have been recognised in the Laurentian lime- 

 stones, which indicate the presence at least of one of the 

 lower types of marine animals. Where animal life is, we 

 may fairly infer the existence of vegetable life as well, 

 since the plant is the only producer of food for the ani- 

 mal. But we are not left merely to this inference. Great 

 quantities of carbon or charcoal in the form of the sub- 

 stance known as graphite or plumbago exist in the 

 Laurentian. Now, in more recent formations we have 

 deposits of coal and bituminous matter, and we know 

 that these have arisen from the accumulation and slow 

 putrefaction of masses of vegetable matter. Further, in 

 places where igneous action has affected the beds, we 

 find that ordinary coal has been changed into anthracite 

 and graphite, that bituminous shales have been converted 

 into graphitic shales, and that cracks filled with soft 

 bituminous matter have ultimately become changed into 

 veins of graphite. When, therefore, we find in the Lau- 

 rentian thick beds of graphite and beds of limestone 

 charged with detached grains and crystals of this sub- 

 stance, and graphitic gneisses and schists and veins of 

 graphite traversing the beds, we recognise the same 

 phenomena that are apparent in later formations con- 

 taining vegetable debris. 



The carbon thus occurring in the Laurentian is not 

 to be regarded as exceptional or rare, but is widely dis- 

 tributed and of large amount. In Canada more especially 

 the deposits are very considerable. 



The graphite of the Laurentian of Canada occurs both 

 in beds and in veins, and in such a manner as to show 

 that its origin and deposition are contemporaneous with 

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