Read Ebook: Note sur une Méthode pour la Réduction d'Intégrales Définies et sur son Application à Quelques Formules Spécials by Haan D Bierens De David Bierens

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When palaeozoic land-plants have been converted into graphite, they sometimes perfectly retain their structure. Mineral charcoal, with structure, exists in the graphitic coal of Rhode Island. The fronds of ferns, with their minutest veins perfect, are preserved in the Devonian shales of St. John, in the state of graphite; and in the same formation there are trunks of Conifers in which the material of the cell-walls has been converted into graphite, while their cavities have been filled with calcareous spar and quartz, the finest structures being preserved quite as well as in comparatively unaltered specimens from the coal-formation. 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 the existence of land-plants. This graphite is composed of contorted and slickensided laminae, much like those of some bituminous shales and coarse coals; and in these 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 uncertain; and it is not as yet fully ascertained 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.

"Acadian Geology," p. 535. In calcined specimens the structures remain in the graphite after decalcification by an acid.

There is thus no absolute impossibility that distinct organic tissues may be found in the Laurentian graphite, 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 the Laurentian period the vegetation of the land may have consisted wholly of cellular plants, as, for example, mosses and lichens; and if so, there would be comparatively little hope of the distinct preservation of their forms or tissues, or of our being able to distinguish the remains of land-plants from those of Algae.

We may sum up these facts and considerations in the following statements: First, that somewhat obscure traces of organic structure can be detected in the Laurentian graphite; secondly, that the general arrangement and microscopic structure of the substance corresponds with that of the carbonaceous and bituminous matters in marine formations of more modern date; thirdly, that if the Laurentian graphite has been derived from vegetable matter, it has only undergone a metamorphosis similar in kind to that which organic matter in metamorphosed sediments 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 probability of its vegetable origin; fifthly, that when we consider the immense thickness and extent of the Eozoonal and graphitic limestones and iron-ore deposits of the Laurentian, if we admit the organic origin of the limestone and graphite, we must be prepared to believe that the life of that early period, though it may have existed under low forms, was most copiously developed, and that it equalled, perhaps surpassed, in its results, in the way of geological accumulation, that of any subsequent period.

Many years ago, at the meeting of the American Association in Albany, the writer was carrying into the room of the Geological Section a mass of fossil wood from the Devonian of Gasp?, when he met the late Professor Agassiz, and remarked that the specimen was the remains of a Devonian tree contemporaneous with his fishes of that age. "How I wish I could sit under its shade!" was the smiling reply of the great zo?logist; and when we think of the great accumulations of Laurentian carbon, and that we are entirely ignorant of the forms and structures of the vegetation which produced it, we can scarcely suppress a feeling of disappointment. Some things, however, we can safely infer from the facts that are known, and these it may be well to mention.

The climate and atmosphere of the Laurentian may have been well adapted for the sustenance of vegetable life. We can scarcely doubt that the internal heat of the earth still warmed the waters of the sea, and these warm waters must have diffused great quantities of mists and vapours over the land, giving a moist and equable if not a very clear atmosphere. The vast quantities of carbon dioxide afterwards sealed up in limestones and carbonaceous beds must also have still floated in the atmosphere and must have supplied abundance of the carbon, which constitutes the largest ingredient in vegetable tissues. Under these circumstances the whole world must have resembled a damp, warm greenhouse, and plants loving such an atmosphere could have grown luxuriantly. In these circumstances the lower forms of aquatic vegetation and those that love damp, warm air and wet soil would have been at home.

If we ask more particularly what kinds of plants might be expected to be introduced in such circumstances, we may obtain some information from the vegetation of the succeeding Palaeozoic age, when such conditions still continued to a modified extent. In this period the club-mosses, ferns, and mare's-tails engrossed the world and grew to sizes and attained degrees of complexity of structure not known in modern times. In the previous Laurentian age something similar may have happened to Algae, to Fungi, to Lichens, to Liverworts, and Mosses. The Algae may have attained to gigantic dimensions, and may have even ascended out of the water in some of their forms. These comparatively simple cellular and tubular structures, now degraded to the humble position of flat lichens or soft or corky fungi, or slender cellular mosses, may have been so strengthened and modified as to constitute forest-trees. This would be quite in harmony with what is observed in the development of other plants in primitive geological times; and a little later in this history we shall see that there is evidence in the flora of the Silurian of a survival of such forms.

It may be that no geologist or botanist will ever be able to realise these dreams of the past. But, on the other hand, it is quite possible that some fortunate chance may have somewhere preserved specimens of Laurentian plants showing their structure.

In any case we have here presented to us the strange and startling fact that the remarkable arrangement of protoplasmic matter and chlorophyll, which enables the vegetable cell to perform, with the aid of solar light, the miracle of decomposing carbon dioxide and water, and forming with them woody and corky tissues, had already been introduced upon the earth. It has been well said that no amount of study of inorganic nature would ever have enabled any one to anticipate the possibility of the construction of an apparatus having the chemical powers of the living vegetable cell. Yet this most marvellous structure seems to have been introduced in the full plenitude of its powers in the Laurentian age.

Whether this early Laurentian vegetation was the means of sustaining any animal life other than marine Protozoa, we do not know. It may have existed for its own sake alone, or merely as a purifier of the atmosphere, in preparation for the future introduction of land-animals. The fact that there have existed, even in modern times, oceanic islands rich in vegetation, yet untenanted by the higher forms of animal life, prepares us to believe that such conditions may have been general or universal in the primeval times we are here considering.

If we ask to what extent the carbon extracted from the atmosphere and stored up in the earth has been, or is likely to be, useful to man, the answer must be that it is not in a state to enable it to be used as mineral fuel. It has, however, important uses in the arts, though at present the supply seems rather in excess of the demand, and it may well be that there are uses of graphite still undiscovered, and to which it will yet be applied.

Finally, it is deserving of notice that, if Laurentian graphite indicates vegetable life, it indicates this in vast profusion. That incalculable quantities of vegetable matter have been oxidised and have disappeared we may believe on the evidence of the vast beds of iron-ore; and, in regard to that preserved as graphite, it is certain that every inch of that mineral must indicate many feet of crude vegetable matter.

It is remarkable that, in ascending from the Laurentian, we do not at first appear to advance in evidences of plant-life. The Huronian age, which succeeded the Laurentian, seems to have been a disturbed and unquiet time, and, except in certain bands of iron-ore and some dark slates coloured with carbonaceous matter, we find in it no evidence of vegetation. In the Cambrian a great subsidence of our continents began, which went on, though with local intermissions and reversals, all through the Siluro-Cambrian or Ordovician time. These times were, for this reason, remarkable for the great abundance and increase of marine animals rather than of land-plants. Still, there are some traces of land vegetation, and we may sketch first the facts of this kind which are known, and then advert to some points relating to the earlier Algae, or sea-weeds.

"Geological Magazine," 1869.

See figure in next chapter.

"Journal of the Geological Society," August, 1881.

Figs. 2, 3, and 4 are drawn from nature by Prof. Penhallow, of McGill College.

"Palaeontologie des Thuringer Waldes," 1856.

See report by the author on "Erian Flora of Canada," 1871 and 1882, for full description of these fossils.

"American Journal of Science," 1878.

Multitudes of markings occurring on the surfaces of the older rocks have been referred to the Algae or sea-weeds, and indeed this group has been a sort of refuge for the destitute to which palaeontologists have been accustomed to refer any anomalous or inexplicable form which, while probably organic, could not be definitely referred to the animal kingdom. There can be no question that some of these are truly marine plants; and that plants of this kind occur in formations older than those in which we first find land-plants, and that they have continued to inhabit the sea down to the present time. It is also true that the oldest of these Algae closely resemble in form plants of this kind still existing; and, since their simple cellular structures and soft tissues are scarcely ever preserved, their general forms are all that we can know, so that their exact resemblance to or difference from modern types can rarely be determined. For the same reasons it has proved difficult clearly to distinguish them from mere inorganic markings or the traces of animals, and the greatest divergence of opinion has occurred in recent times on these subjects, as any one can readily understand who consults the voluminous and well-illustrated memoirs of Nathorst, Williamson, Saporta, and Delgado.

The author of this work has given much attention to these remains, and has not been disposed to claim for the vegetable kingdom so many of them as some of his contemporaries. The considerations which seem most important in making such distinctions are the following: 1. The presence or absence of carbonaceous matter. True Algae not infrequently present at least a thin film of carbon representing their organic matter, and this is the more likely to occur in their case, as organic matters buried in marine deposits and not exposed to atmospheric oxidation are very likely to be preserved. 2. In the absence of organic matter, the staining of the containing rock, the disappearance or deoxidation of its ferruginous colouring matter, or the presence of iron pyrite may indicate the removal of organic matter by decay. 3. When organic matter and indications of it are altogether absent, and form alone remains, we have to distinguish from Algae, trails and burrows similar to those of aquatic animals, casts of shrinkage-cracks, water-marks, and rill-marks widely diffused over the surfaces of beds. 4. Markings depressed on the upper surfaces of beds, and filled with the material of the succeeding layer, are usually mere impressions. The cases of possible exceptions to this are very rare. On the contrary, there are not infrequently forms in relief on the surfaces of rocks which are not Algae, but may be shallow burrows arched upward on top, or castings of worms thrown up upon the surface. Sometimes, however, they may have been left by denudation of the surrounding material, just as footprints on dry snow remain in relief after the surrounding loose material has been drifted away by the wind; the portion consolidated by pressure being better able to resist the denuding agency.

"Impressions and Footprints of Aquatic Animals," "American Journal of Science," 1873.

"Canadian Naturalist," vol. vii.

The name Bilobites was originally proposed by De Kay for a bivalve shell . Its application to supposed Algae was an error, but this is of the less consequence, as these are not true plants but only animal trails.

Supplement to "Acadian Geology."

"Canadian Naturalist," 1864.

I agree with Dr. Williamson in believing that all or nearly all the forms referred to Crossochorda of Schimper are really animal impressions allied to Nereites, and due either to worms or, as Nathorst has shown to be possible, to small crustaceans. Many impressions of this kind occur in the Silurian beds of the Clinton series in Canada and New York, and are undoubtedly mere markings.

"Tracks from Yoredale Rocks," "Manchester Literary and Philosophical Society," 1885.

"Coal Flora of Pennsylvania," vol. iii., Plate 88.

"Journal of the Geological Society," vol. xii., p. 251.

"Acadian Geology," 2d ed., p. 26.

An entirely different kind of shrinkage-crack is that which occurs in certain carbonised and flattened plants, and which sometimes communicates to them a marvellous resemblance to the netted under surface of an exogenous leaf. Flattened stems of plants and layers of cortical matter, when carbonised, shrink in such a manner as to produce minute reticulated cracks. These become filled with mineral matter before the coaly substance has been completely consolidated. A further compression occurs, causing the coaly substance to collapse, leaving the little veins of harder mineral matter projecting. These impress their form upon the clay or shale above and below, and thus when the mass is broken open we have a carbonaceous film or thin layer covered with a network of raised lines, and corresponding minute depressed lines

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