1870.] DAWSON — LAURENTIAN GRAPHITE. 17 



bituminous shales and limestones have been metamorphosed and 

 converted into graphitic rocks not dissimilar to those in the less 

 altered portions of the Lauren tian.f 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 the modern bituminous limestones and shales. 

 Such bituminous veins occur in the Lower Carboniferous lime- 

 stone and shale of Dorchester and Hillsborough, New Brunswick, 

 with an arrangement very similar to that of the veins of graphite ; 

 and in the Quebec rocks of Point Levi, veins attaining to a thick- 

 ness 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 analogies would lead us 

 to infer that the larger part of the Laurentian graphite falls under 

 the second class of deposits above mentioned, and that, if of 

 vegetable origin, the organic matter must have been thoroughly 

 disintegrated and bituminized 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 terrestrial 

 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 substances produced in the decay of plants. In 

 this case such great ore beds as that of Hull, on the Ottawa, 70 

 feet thick, or that near Newborough, 200 feet thick ^, must 

 represent a corresponding quantity of vegetable matter which has 

 totally disappeared. It may be added that similar demands on 

 vegetable matter as a deoxidizing agent are made by the beds and 

 veins of metallic sulphides of the Laurentian, though some of the 

 latter are no doubt of later date than the Laurentian rocks 

 themselves. 



It would be very desirable to confirm such conclusions as 

 those above deduced by the evidence of actual microscopic 

 structure. It is to be observed, however, that when, in more 

 modern sediments. Algae have been converted into bituminous 

 matter, we cannot ordinarily obtain any structural evidence of 

 the origin of such bitumen, and in the graphitic slates and lime- 



* " Geology of Canada," 1863. 



Vol. Y. B Ko. 1 



