OLDEST of all the formations known to ge representing perhaps the earliest rocks produ earth had ceased to be a molten mass, are th talline, and much-contorted rocks named by W. E. Logan Laurentian, and which are large in the northern parts of North America and in many other regions. So numerous and e deed, are the exposures of these rocks, that w reason to believe that they underlie all the tions of our continents, and are even world-w distribution. In the lower part of this grea rocks which, in some places at least, is thir feet in thickness, we find no traces of the any living thing on the earth. But, in the tion of the Laurentian, rocks are found wh that there were already land and water, and tha and possibly the land were already tenante beings. The great beds of limestone which part of the system furnish one indication of t later geological formations the limestones ar ganic-that is, they consist of accumulated shells, corals, and other hard parts of mari which are composed of calcium carbonate, wh mals obtain directly from their food, and ind the calcareous matter dissolved in the sea-wat

manner great beds of iron-ore exist in the Laurentian ; but in later formations the determining cause of the accumulation of such beds is the partial deoxidation and solution of the peroxide of iron by the agency of organic matter. Besides this, certain forms known as Eozoon Canadense have been recognised in the Laurentian limestones, which indicate the presence at least of one of the lower types of marine animals. Where animal life is, we may fairly infer the existence of vegetable life as well, since the plant is the only producer of food for the animal. But we are not left merely to this inference. Great quantities of carbon or charcoal in the form of the substance known as graphite or plumbago exist in the Laurentian. Now, in more recent formations we have deposits of coal and bituminous matter, and we know that these have arisen from the accumulation and slow putrefaction of masses of vegetable matter. Further, in places where igneous action has affected the beds, we find that ordinary coal has been changed into anthracite and graphite, that bituminous shales have been converted into graphitic shales, and that cracks filled with soft bituminous matter have ultimately become changed into veins of graphite. When, therefore, we find in the Laurentian thick beds of graphite and beds of limestone charged with detached grains and crystals of this substance, and graphitic gneisses and schists and veins of graphite traversing the beds, we recognise the same phenomena that are apparent in later formations containing vegetable débris.

The carbon thus occurring in the Laurentian is not to be regarded as exceptional or rare, but is widely distributed and of large amount. In Canada more especially the deposits are very considerable.

The graphite of the Laurentian of Canada occurs both in beds and in veins, and in such a manner as to show that its origin and deposition are contemporaneous with

C

those of the containing rock. Sir William L that "the deposits of plumbago generally limestones or in their immediate vicinity, a varieties of the rock often contain large cryst of plumbago. At other times this mineral disseminated as to give a bluish-grey colour stone, and the distribution of bands thus col. to mark the stratification of the rock." states: "The plumbago is not confined to stones; large crystalline scales of it are occa seminated in pyroxene rock, and sometimes and in feldspathic rocks, or even in magnet iron." In addition to these bedded forms, th true veins in which graphite occurs associate cite, quartz, orthoclase, or pyroxene, and eit seminated scales, in detached masses, or in ban

separated from each other and from the w feldspar, pyroxene, and quartz." Dr. Hunt tions the occurrence of finely granular variet that peculiarly waved and corrugated variety fossil wood, though really a mere form of structure, which also occurs at Warrensburg, I and at the Marinski mine in Siberia. Many of are not true fissures, but rather constitute a 1 shrinkage cracks or segregation veins traversing less numbers the containing rock, and most in their dimensions, so that they often resemble nodular masses. It is most probable that the g the veins was originally introduced as a liquid hydrocarbon; but in whatever way introduced, acter of the veins indicates that in the case of tl number of them the carbonaceous material n been derived from the bedded rocks traversed veins, to which it bears the same relation with

* "Geology of Canada," 1863.

LAURENTIAN AND EARLY PALEOZOIC.

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of bitumen found in the bituminous shales of the Carboniferous and Silurian rocks. Nor can there be any 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. Some years ago, in the township of Buckingham, on the Ottawa River, 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 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 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 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.

scarcely an exaggeration to maintain that the carbon in the Laurentian is equal to that in of the Carboniferous system. It is also to that an immense area in Canada appears to by these graphitic and Eozoon limestones, an graphitic deposits exist in the continuation tem in the State of New York, while in rock be of this age near St. John, New Brunswick very thick bed of graphitic limestone, and ass it three regular beds of graphite, having a thickness of about five feet.*

It may fairly be assumed that in the pro and in those geological periods with whose. mains we are more familiar than with those rentian, there is no other source of unoxidized rocks than that furnished by organic matte this has obtained its carbon in all cases, in stance, from the deoxidation of carbonic aci plants. No other source of carbon can, I imagined in the Laurentian period. We may suppose either that the graphitic matter of the has been accumulated in beds like those of co it has consisted of diffused bituminous matter that in more modern bituminous shales and and oil-bearing limestones. The beds of gra St. John, some of those in the gneiss at Ticor New York, and at Lochaber and Buckingham where in Canada, are so pure and regular that fairly compare them with the graphitic coal Island. These instances, however, are except the greater part of the disseminated and vein might rather be likened in its mode of occurre bituminous matter in bituminous shales and lin

*Matthew in "Quarterly Journal of the Geological S "Acadian Geology," p. 662.