LAURENTIAN AND EARLY PALAEOZOIC, 



13 



We may compare the disseminated graphite to that 

 which we find in those districts of Canada in which Silu- 

 rian and Devonian bituminous shales and limestones have 

 been metamorphosed and converted into graphitic rocks 

 not very dissimilar to those in the less altered portions of 

 the Laurontian.* In like manner it seems probable that 

 the numerous reticulating veins of graphite may have 

 been formed by the segregation of bituminous matter into 

 fissures and planes of least resistance, in the manner in 

 which such veins occur in modern bituminous limestones 

 and shales. Such bituminous veins occur in the Lower 

 Carboniferous limestone and shale of Dorchester and 

 Hillsborough, New Brunswick, with an arrangement very 

 similar to that of the veins of graphite ; and in the Que- 

 bec rocks of Point Levi, veins attaining to a thickness of 

 more than a foot, are filled with a coaly matter having a 

 transverse columnar structure, and regarded by Logan 

 and Hunt as an altered bitumen. These palaeozoic analo- 

 gies would lead us to infer that the larger part of the 

 Laurentian graphite falls under the second class of de- 

 posits above mentioned, and that, if of vegetable origin, 

 the organic matter must have been thoroughly disin- 

 tegrated and bituminised before it was changed into 

 graphite. This would also give a probability that the 

 vegetation implied was aquatic, or at least that it was 

 accumulated under water. 



Dr. Hunt has, however, observed an indication of ter- 

 restrial vegetation, or at least of subaerial decay, in the 

 great beds of Laurentian iron-ore. These, if formed in 

 the same manner as more modern deposits of this kind, 

 would imply the reducing and solvent action of sub- 

 stances produced in the decay of plants. In this case 

 such great ore-beds as that of Hull, on the Ottawa, seventy 



* Granby, Melbourne, Owl's Head, &c., " Geology of Canada," 1863, 

 p. 699. 



