LAURENTIAN AND EARLY PALAEOZOIC. 



11 



of bitumen found in the bituminous shales of the Car- 

 boniferous and Silurian rocks. Nor can there be any 

 doubt that the graphite found in the beds has been de- 

 posited along with the calcareous matter or muddy and 

 sandy sediment of which these beds were originally com- 

 posed.* 



The quantity of graphite in the Lower Laurentian 

 series is enormous. Some years ago, in 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 six hundred feet or 

 more, and was found to be filled with disseminated crys- 

 tals of graphite and yeins 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 twenty to thirty feet. In the 

 adjoining township of Lochaber Sir W. E. Logan notices 

 a band from twenty-five to thirty feet thick, reticulated 

 with graphite veins to such an extent as to be mined with 

 profit for the mineral. At another place in the same dis- 

 trict a bed of graphite from ten to twelve feet thick, and 

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

 As it appears in the excavation made by the quarrymen, 

 it resembled a bed of coal ; and a block from this bed, 

 about four feet thick, was a prominent object in the 

 Canadian department of the Colonial Exhibition of 1886. 

 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 aggregate thickness of thirty-five hundred feet, it is 



* Paper by the author on Laurentian Graphite, " Journal of London 

 Geological Society," 1876. 



