114 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
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 enor- 
mous. In a recent visit to the township of Buckingham, on the 
Ottawa River, I examined a band of limestone believed to be a con- 
tinuation of that described by Sir W. E. Logan as the Green Lake 
Limestone. It was estimated to amount, with some thin inter- 
stratified 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 
adjoining township of Lochaber Sir W. EK. 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 
place in the same district a bed of graphite from 10 to 12 feet thick, 
and yielding 20 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 Hozoon-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, 
haying an aggregate thickness of about 5 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 un- 
oxidized 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. 
We may, however, suppose either that the graphitic matter of the 
Laurentian has been accumulated in beds like those of coal, or that 
it has consisted of diffused bituminous matter similar to that in more 
modern bituminous shales and bituminous and oil-bearing lme- 
stones. The beds of graphite near St. John, some of those in the 
gneiss at Ticonderoga in New York, and at Lochaber and Buck- 
ingham and elsewhere in Canada are so pure and regular that one 
might fairly compare them with the graphitic coal of Rhode Island. 
These instances, however, are exceptional, and the greater part of 
the disseminated and vein graphite might rather be compared in its 
* Matthew in ‘ Quart. Journ. Geol. Soe.’ vol. xxi. p. 423. Acadian Geology, 
p. 662. 
