16 THE CANADIAN NATURALIST. [Marcll 



place in the same district a bed of graphite from 10 to 12 feet 

 thick, and yielding 20 per cent, of the pure material, is worked. 

 When it is considered that graphite occurs in similar abundance 

 at several other horizons, in beds of limestone which have been 

 ascertained by Sir W. E. Logan to have an aggreate thickness of 

 3500 feet, it is scarcely an exaggeration to maintain that the 

 quantity of carbon in the Laurentian is equal to that in similar 

 areas of the Carboniferous system. It is also to be observed that an 

 immense area in Canada appears to be occupied by these graphitic 

 and ^o2;oo?i-limestones, and that rich graphitic deposits exists in 

 the continuation of this system in the state of New York, while 

 in rocks believed to be of this age near St. John, New Brunswick, 

 there is a very thick bed of graphitic limestone, and associated 

 with it three regular beds of graphite, having an aggregate 

 thickness of about five feet.* 



It may fairly be assumed that in the present world and in 

 those geological periods with whose organic remains we are more 

 familiar than with those of the Laurentian, there is no other 

 source of unoxidized carbon in rocks than that furnished by 

 organic matter, and that this has obtained its carbon in all cases, 

 in the first instance, from the deoxidation of carbonic acidl)y 

 living plants. No other source of carbon can, I believe, be 

 imagined in the Laurentian period. We may, however, suppose 

 either that the graphitic matter of the Laurentian has been 

 accumulated in beds like those of coal, or that it has consisted of 

 difi'used bituminous matter similar to that in more modern 

 bituminous shales and bituminous and oil-bearing limestones. 

 The beds of graphite near St. John, some of those in the gneiss 

 at Ticonderoga in New York, and at Lochaber, Buckingham, 

 and elsewhere in Canada are so pure and regular that one might 

 fairly compare them with the graphitic coal of llhode Island. 

 These instances, however, are exceptional, and the greater part 

 of the disseminated and vein graphite might rather be compared 

 in its mode of occurrence to the bituminous matter in bituminous 

 shales and limestones. 



We may compare the disseminated graphite to that which we 

 find in those districts of Canada in which Silurian and Devonian 



* Matthew in " Quart. Joum. Geol- Soc," vol. xxi. p. 423. " Acadian 

 Geology, p. 662." 



t Granby, Melbourne, Owl's Head, &c., " Geology of Canada," 1863, 

 p. 529. 



