THE LAUEENTIAN ROCKS. 29 



" The quantity of graphite in the Lower Laurentian series is 

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

 on the Ottawa Eiver, 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 ex- 

 tent 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 district a bed of graphite from ten to twelve 

 feet thick, and yielding twenty 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 

 aggregate 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 Eozoon limestones, and 

 that rich graphitic deposits exist 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 



* Matthew, in Quart. Journ. Geol. Soc., vol. xxi., p. 423. Acadian 

 Geology, p. 662. 



