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rocks there are three great limestone layers, separated by gneissoid rocks, aggre- 
gating not less than 3,500 feet in thickness. ‘The limestone of each of these 
layers is often mixed with, or passes into, rocks which consist largely of 
pyroxene, or hornblende, and these portions abound frequently with valuable 
minerals, the most common being mica and graphite. 
As to the probable origin of the graphite in these rocks, Dr. Dawson 
remarks that “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 
cases, in the first instance, from the deoxidation of carbonic acid by living plants, 
No other source of carbon can, I believe, be imagined in the Laurentian period.” 
When we come to consider the enormous deposits of carbon held by the 
Laurentian rocks, it will easily be seen that immense periods, even of a most 
prolific vegetation, must have been necessary for their formation. ‘The atmos- 
phere of that period must have contained a great amount of carbonic acid, and 
the seas have been charged with abundance of carbonate of lime, and have con- 
tained, in common with the land surface, enormous expanses of vegetable life. 
The amount of carbon, in the form of graphite, in the Laurentian system, is con- 
sidered by Dawson to equal that (in the form of coal) of equal areas in the 
carboniferous. 
In the Township of Buckingham a band of limestone, with some thin inter- 
stratified bands of gneiss, about six hundred feet in thickness, occurs, and is filled 
to such an extent with veins, or disseminated crystals and scales of graphiie, 
that the mineral is estimated to constitute one-fourth of the whole in places, and, 
allowing for the poverty of some portions, the total vertical thickness of pure 
graphite can not be less than from 20 to 30 feet. It occurs in equal abundance 
at several other horizons in beds of limestone, estimated by Logan to have an 
aggregate thickness of 3,500 feet; and the total quantity thus contained can 
readily be seen to be enormous. 
Unlike beds of coal, which occupy the place where the forests which pro- 
duced them formerly flourished, graphite has been disseminated through the 
rocks by changes therein. In some piaces, to be sure, beds are found so regular 
and pure that they may be fairly compared to deposits of anthracite; but these 
are the exceptions; the great bulk of the mineral is scattered in scales, lumps or 
thin veins. Many of these veins are mere shrinkage cracks, traversing in 
countless numbers the containing rocks, and so irregular in size as often to 
resembie strings of nodular masses. 
The graphite contained in these is supposed to Lave flowed into them in the 
form of a hydro-carbon ; or it may have been in a state of aqueous solution at an 
enormous heat. It is evidently derived from the rocks traversed by the veins, and 
has deposited with it sediment from these beds. Hence there is no occurrence of 
fossils as in coal, and the vegetable origin of graphite can only be inferred from 
analogy, and from the fact of a few scanty organic remains, as Wie of eozoon, 
having been found in the containing rocks. . “3 - 
The graphite of the Buckingham district occurs in three distinct forms, 
always in or in close proximity t o bands of crystalline limestone. First, in foli- 
ated scales or plates in limestone, gneiss, pyroxene or quartzite, and sometimes 
even in iron ores, as is the case at Hull; secondly, in distinct embe dded masses, 
or pockets in the limestones; thirdly, in veins traversing in every direction the 
containing rock. 
The first form is most common, and occurs in greatest abundance in the 
limestones, often forming such large deposits as to possess great economic value, 
as at Buckingham. . 
The second form is of common occurrence, and has been worked in Buck- 
ingham and Lochaber, where the deposits are considerable. In the latter town- 
