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Lorsque le document est trop grand pour dtre reproduit en un seul cliche, il est film6 d partir de Tangle supdrieur gauche, de gauche d droite, et de haut en bas, en prenant le nombre d'images n6cessaire. Les diagrammes suivants illustrent la mdthode. 1 2 3 1 2 3 4 5 6 M-nTErCTP::^ • --. ^ '^ ^ « I iiL ^7^6 A From the Quarterly Journai of the Gbolooical Society for February 1870.] ON THE GRAPHITE or THE LAURENTIAN OF CANADA. BY J. W. DAWSON, LL.D., F.R.S., F.G.S. lU As , 1 J In my paper of 1>'(;4, on the Organic llemains of the Laurentian Limestones of Canada, as a sequel to Che description of Eozoon Canadcnsi', I noticed, among other indications of organic matters in these limestones, the presence of films and fibres of graphitic matter, and insisted on the probability that at least some of the lower forms of plant Hie must have existed in the seas in which gigantic Fora- minifora could flourish. Dr. Hunt had previously, on chemical evidence, inferred the existence of Laurentian vegetation*, and Dana had argued as to the probability of this on various grounds f; and my object in referring to these indications in 18G4, as well as to the supposed burrows of annelids, subsequently described by me J, was to show that the occurrence of Eozoon was not to be regarded as altogether isolated and unsupported by probabilities of the ex- istence of organic remains in the Laurentian deducible from other considerations. Now that the questions which have been raised regarding Eozoon * 'American Journal of Science' (2), xxxi. p. 395. From this article, written in 18(51, after the announcement df the existence of laminated forms supposed to be orgnnic in the Ljiurentian, by Sir W. E. Logan, but before their structure and afTinitics had been ascertained. I quote the following sentences: — " We see in the Laurentian series bods and veins of metallic sulphurets, precisely as in more recent formations ; and the extensive beds of iron-ore, hundreds of feet thick, which abound in that ancient system, correspond not only to great volumes of strata dejirived of that metal, but, as we may suppose, to organic matters whicli, but for the then gr at diffusion of iron-oxyd in conditions favourable for their oxydation, might have formed deposits of mineral carbon far more extensive than those beds of plumbago which we actually meet in the Laurentian strata. All these conditions load us then to conclude the existence of an abundant vegetivtion during the Laurentian period." t Manual of Geology. I may also be permitted to refer to my own work ' Archaia,' p. lOS, and Appendix U, 1860. I Quart. Journ. Geol. Soc. vol. xxii. p. 608. ^ii;4 DAWSON— LAURENTI AN ORAPMITE. 113 may be coiDsidoivd settled, not only by the adhesion of the greatest authorities in palicontology and zoology, l)ut by the discovery of similar organisms in roeks of the same age elsewjiere, by specimens preserved in such a nmnner us to avoid all the objections raised to the mineral condition of the fossil*, and by the discovery of such modern analogies as that furnished by Batlnih'ms, it may be pioper to invite the attention of geologists more particularly to tlie evidence of vegetable life aflbrded by the deposits of graphite existing in the Laurentian. 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 depo- sition are contemporaneous with those of the containing rock. Sir William Logan states f that "the deposits of plumbago generally occur in the limestones or in their immediate nciuity, and granular varieties of the rock often contain large crystalline i)lates of plum- bago. At other times this mineral is so finely disseminated as to give a bluish-gray colour to the limestone, and the distribution of baiuls thus coloured, seems to mark the stratification of tlie lock." He further states: — "The i>lumbag() is not confined to the lime- stones; large crystalline seales of it are occasionally disseminated in ])yroxene rock or pyrallolite, and sometimes in (). 114 i'KUUKEDIHruS OV 'rU£ OKOLOUICAL 80CIKTY. been doposited along with tbo calcareous matter or muddy and sandy bediment of which these bods were originally composed. The quantity of graphite in the Ix)wer Laurentian series is enor- mous. In a recent visit to the township of liuckinghum, 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 (500 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 bund cannot contain in all a less vertical thickness of pure grai)hite than from 20 to 30 feet. In the adjoining township of Lochaber Sir W. E. 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 \V. 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 ap])ears to be occupied by these grapliitiu and /Joroon-limestones, and that rich gra])hitic deposits exist in the continuation of this system in the State of New York, while in rocks believed to be of this ago near St. John, New Brunswick, there is a very thick bed of graj)hitic linu'stone, and associated with it three regular beds of grapliite, having an aggregate thickness of about 5 f'^et*. It may fairly bo assumed that in the present world and in those geological periods with whose organic remains wc 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, bo imagined in the Laurentian period. We may, however, suppose either that the graphitic matter of the Laurentian has been accumula.ed 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 lime- 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 ? Ir * Matthew in ' Quart. Journ. Geol. See' vol. xxi. p. 423. p. G02. Acadian Geology, DAWSON — LAUEENTIAN ORAPniTE. 115 mode of occurrence to the bituminous matter in bituminous shaloa and limestones. We may compare the disseminated graphite to that which wo find in those districts of Canada in which Siluiian and Devonian bituminous shales and limestones have been metamorphosed and converted into graphitic rocks not dissimilar to those in the less altered portions of the Laurentian*. In like manner it seems pro- bable that the numerous reticulating veins of graphite may have been formed by the segregation of bituminous matter into fi jsurcs and planes of least resistance, in the manner in which such veins occur in modern bituminous limestones and shales. 8uch bitumi- nous veins occur in the Lower Carboniferous limestone and shale of Dorchester and Hillsborough, New Brunswick, with an arrangement very similar to that of the veins of graphite ; and in the Quebec rocks of Point Levi, veins attaining to a thickness of more than a foot, are filled with a coaly matter having a transverse columnar structure and regarded by Logan and Hunt as an altered bitumen. These paloeozoic analogies would lead us to infer that the larger part of the Laurentian graphite ulls under the second class of deposits above mentioned, and that, if of vegetable origin, the organic matter must have been thoroughly disintegrated and bituminized before it was changed into graphite. This would also give a pro- bability that the vegetation implied was aquatic, or at least that it was accumulated under water. Dr. Hunt has, however, observed an indication of terrestrial vege- tation, or at least of subacrial decay, in the great beds of Laurentian iron-ore. These, if formed in the same manner as more modern deposits of this kind, would imply the reducing and solvent action of substances produced in the decay of plants. In this case such great ore beds as that of Hull, on the Ottawa, 70 feet thick, or that near Newborough, 200 feet thick f, must represent a corresponding quantity of vegetable matter which has totally disappeared. It may •be added that similar demands on vegetable matter as a deoxidizing agent are made by the beds and veins of metallic sulphides of the Laurentian, though some of the latter are no doubt of later date than the Laurentian rocks themselves. It would be very desirable to confirm such conclusions as those above deduced by the evidence of actual microscopic structure. It is to be observed, however, that when, in more modern sediments, Alga3 have been converted into bituminous matter, we cannot ordi- narily obtain any structural evidence of the origin of such bitumen, and in the graphitic slates and limestones derived from the metamor- phosis of such rocks no organic structure remains. It is true that, in certain bituminous shales and limestones of the Silurian system, shreds of organic tissue can sometimes be detected, and in some cases, as in the Lower Silurian limestone of the La Cloche moun- tains in Canada, the pores of brachiopodous shells and the cells of corals have been penetrated by black bituminous matter, forming * Granbv, Melbourne, Owl's Head. &c., ' Geology of Canada; 1863, p. 599. t Geology of Canada, 1863. -J,i 11(5 PRUCEEDINOS OF TffE OKO LOGICAL SOCIKTT. \*liiit may be regartled tw naturul injections, somctinies of much bonuty. In correspondence with tliis, while in some Laurentinn giiiphitic roc s, as, for instance, in tho compact graphite of Cla- rendon, the carbon presentH a curdled appearance due to segregation, and precisely similar to that of the biiumen in more modern bitu- minous rocks, I can detect in tho graphitic limestones occasional fibrous structures which may be remains of plants, and in some specimens vermicular lines, which I believe to be tubes of Kozoon penetrated by matter once bituminous, but now in the state of graphite. When palicozoic land-plants have been converted into graphite, they sometimes perfectly retain their structure. Jkfineral cliarcoal, with structure, exists in tho graphitic coal of Rhode Island. Tho fronds of ferns, with their minutest veins perfect, are preserved in the Devonian shales of St. John, in tho state of graphit<; ; and in tho same formation there are trunks of Conifers {Dado.rtjlon onaixjon- dianum) in whioh the material of the cell- walls has been converted into graphite, while their canties have been filled with calcareous spar and (piartz, the finest structures being preserved (piite as well as in comparatively unaltered specimens from the co.il-forniation*. No structures so perfect have as yet been detected in the Laurentian, though in the largest of the three graphitic beds at St. John there appear to be fibrous structures, which I believe may indicate tho existence of land-plants. This graphite is composed of contorted and slickensided lamina), much like those of some bituminous shales and coarse coals ; and in these there are occasional small pyritous masses which show hollow carbonaceous fibres, in some cases presenting obscure indications of lateral pores. I regard these indications, however, as unceiiaiu ; and it is not as yet fully iusccr- tained that these beds at St. John are on the same geological horizon with the Lower Laurentian of Canada, though they certainly underlie the Primordial series of the Acadian group, and are separated from it by beds having the character of the Huronian. There is thus no absolute impossibility that distinct organic tissues may be found in the Laurentian gra])hite, if formed from land-plants, more especially if any plants existed at that time having true woody or vascular tissues ; but it cannot with certainty be affirmed that such tissues have been found. It is possible, however, that in tho Laurentian period tho vegetation of tho land may have consisted wholly of cellular plants, as, for example, mosses and lichens ; and if so, there would bo comparatively little hope of tho distinct pre- servation of their forms or tissues, or of our being able to distinguish the remains of land-plants from those of Alga\ We may sum up these facts and considerations in tho following statements : — First, that somewhat obscure traces of organic struc- ture can be detected in the Laurentian gra])hite ; secondly, that the general arrangement and microscopic structure of the substance cor- responds with that of the carbonaceous and bituminous matters in * Acadian Geology, p. 535. In calcified spLviinens the structures remain in tho grnphiU> after dct'nli-iflr'nfion hy nn acid. -hi DAWSON — LAUHENTIAW OUArHrrK. 117 nmriiio fonuntions of more modern date; thirdly, that if the Lau- itutijiii graphite liu.s be(;n dorivc.'d from vegetable matter, it has only undergone a metumorphoHiH Himiliir in kind to tha^ which organic matter in metamori)ho8ed sedimciiit of later age has experienced ; fourthly, that the association of the graphitic matter with organic limestone, beds of iron ore, and metallic sulphides greatly strengthens the ])robability of its vegetable origin ; fifthly, tliat when wo con- sider the immense thickness and extent of the Ko/.oonal and grapliitic limestones and iron-ore deposits of the Laurentian, if we admit the organic origin of the limestone and graphite, we must be prepared to belic've that the life of that early period, though it may havo existcul under low forms, was most copiously developed, and that it ecpuUled, perhaps surpassed, in its results, in the way of geological accumulation, that of any subsefjuent period. In conclusion, this subject opens up several interesting fields of chemical, physiological, and geological inciuiry. One of these relates to the conclusions stated by Dr. Hunt as to the })robable existence of a large amount of carbonic acid in the Laurentian atmosphere, and of much carbonate of lime in the seas of that jxjriod, and the possible relation of this to the abundance of certain low forms of plants and animals. Another is the comparison already instituted by Professor Huxley and Dr. Carjienter, between the conditions of the Laurentian and those of the deeper parts of the modern ocean. Another is the possible occurrence of other forms of animal life than Eozoon and Annelids, which I have stated in my paper of 1&G4, after extensive microscopic study of the Laurentian limestones, to be indicated by the occurrence of calcareous fragments, differing in structure from Eozoon, but at present of unknown iiature. Another is the efltbrt to bridge over, by further discoveries similar to that of the Eozoon havaricum of (iiimbel, the gap now existing between the life of the Lower- Laurentian and that of the Primordial Silurian or Cambrian period. It is scarcely too much to say that these incjuiries open up a new world of thought and investigation, and hold out the hope of bringing us into the presence of the actual origin of organic life on our planet, though this may perhaps })c found to have been Prelaurentian. I would here take the opportunity of stating that, in proposing the name Eozoon for the first fossil of the Laurentian, and in suggesting for the period the name " P]ozoic," 1 have by no means desired to exclude the possibility of forms of life which may have been precursors of what is now to us the dawn of organic existence. Should remains of still older organisms be found in those rocks now known to us onl}- by pebbles in the Laurentian, these names wdll at least serve to mark an important stage in geological investigation.