1870.] DAWSON — LAURENTIAN GRAPHITE. 15 



sometimes in quartzite and in feldspathic rocks, or even in 

 mae:netic oxide of ii'on." In addition to these bedded forms, 

 there are also true veins in which graphite occurs associated with 

 calcite, quartz, orthoclase, or pyroxene, and either in disseminated 

 scales, in detatched masses, or in bands or layers " separated from 

 each other, and from the wall rock by feldspar, pyroxene, and 

 quartz." Dr. Hunt also mentions the occurrence of finely gran- 

 ular varieties, and of that peculiarly waved and corrugated variety 

 simulating fossil wood, though really a mere form of laminated 

 structure, which also occurs at Warrensburgh, New York, and at 

 the Marinski mine in Siberia. Many of the veins are not true 

 fissures, but rather constitute a net- work of shrinkage cracks or 

 segregation veins traversing in countless numbers the containing 

 rock, and most irregular in their dimensions, so that they often 

 resemble strings of nodular masses. It has been supposed 

 that the graphite of the veins was originally introduced as a liquid 

 hydro-carbon. Dr. Hunt, however, regards it as possible that it 

 may have been in a state of aqueous solution^ at a heat approach- 

 ing ignition; but in whatever way introduced, the character of 

 the veins indicates that in the case of the greater number of 

 them the carbonaceous material must have been derived from the 

 bedded rocks traversed by these veins, while there can be no doubt 

 that the graphite found in the beds has been deposited along with 

 the calcareous matter or muddy and sandy sediment of which 

 these beds were originally composed. 



The quantity of graphite in the Lower Laurentian series is 

 enormous. In a recent visit to the township of Buckingham, on 

 the Ottawa Kiver, I examined a band of limestone believed to be 

 a continuation of that described by Sir W. E. Logan as the Green 

 Lake Limestone. It was estimated to amount, with some thin 

 interstratified bands of gneiss, to a thickness of 600 feet or more, 

 and was found to be filled with disseminated crystals of graphite 

 and veins of the mineral to such an extent as to constitute in some 

 places one-fourth of the whole ; and making every allowance for 

 the poorer portions, this band cannot contain in all a less vertical 

 thickness of pure graphite than from 20 to 30 feet. In the ad- 

 joining township of Eochaber Sir W. E. Logan notices a band 

 from 25 to 30 feet thick, reticulated with graphite veins to such 

 an extent as to be mined with profit for the mineral. At another 



* <( 



Report of the Geological Survey of Canada,' 1866, p. ^'33. 



