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materials of this kind should constitute considerable portions of such vegetable accumulations as the beds of coal, and that when present in large proportion they should afford richly bituminous beds. All this agrees with the fact, apparent on examination of the common coal, that the greater number of its purest layers consist of the flattened bark of Sigillaria and similar trees, just as any single flattened trunk embedded in shale becomes a layer of pure coal. It also agrees with the fact that other layers of coal, and also the cannels and earthy bitumens, appear under the microscope to consist of finely comminuted particles, principally of epidermal tissues, not only from the fruits and spore-cases of plants, but also from their leaves and stems. These considerations impress us, just as much as the abundance of sporecases, with the immense amount of the vegetable matter which has perished during the accumulation of coal, in comparison with that which has been preserved.

I am indebted to Dr. T. Sterry Hunt for the following very valuable information, which at once places in a clear and precise light the chemical relations of epidermal tissue and spores with coal. Dr. Hunt says: "The outer bark of the cork-tree, and the cuticle of many if not all other plants, consists of a highly carbonaceous matter, to which the name of suberin has been given. The spores of Lycopodium also approach to this substance in composition, as will be seen by the following, one of two analyses by Duconi,* along with which I give the theoretical composition of pure cellulose or woody fibre, according to Payen and Mitscherlich, and an analysis of the suberin of cork, from Quercus suber, from which the ash and 2.5 per cent of cellulose have been deducted.t

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"This difference is not less striking when we reduce the above centesimal analyses to correspond with the formula of cellulose, C24H20020, and represent cork and Lycopodium as containing twenty-four equivalents of carbon. For comparison I give the composition of specimens of peat, brown coal, lignite, and bituminous coal :

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"It will be seen from this comparison that, in ultimate composition, cork and Lycopodium are nearer to lignite than to woody fibre, and may be converted into coal with far less loss of carbon and hydrogen than the latter. They in fact approach closer in composition to resins and fats than to wood, and, moreover, like those substances repel water, with which they are not easily moistened, and thus are able to resist those atmospheric influences which effect the decay of woody tissue."

I would add to this only one further consideration. The nitrogen present in the Lycopodium spores, no doubt, belongs to the protoplasm contained in them, a substance which would soon perish by decay; and subtracting this, the cell-walls of the spores and the walls of the spore

*"Canadian Naturalist," vi., 253.

cases would be most suitable material for the production of bituminous coal. But this suitableness they share with the epidermal tissue of the scales of strobiles, and of the stems and leaves of ferns and lycopods, and, above all, with the thick, corky envelope of the stems of Sigillariæ and similar trees, which, as I have elsewhere shown,* from its condition in the prostrate and erect trunks contained in the beds associated with coal, must have been highly carbonaceous and extremely enduring and impermeable to water. In short, if, instead of "spore-cases, we read "epidermal tissues in general, including sporecases," all that has been affirmed regarding the latter will be strictly and literally true, and in accordance with the chemical composition, microscopical characters, and mode of occurrence of coal. It will also be in accordance with the following statement, from my paper on the "Structures in Coal," published in 1859:

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"A single trunk of Sigillaria in an erect forest presents an epitome of a coal-seam. Its roots represent the Stigmaria underclay; its bark the compact coal; its woody axis the mineral charcoal; its fallen leaves (and fruits), with remains of herbaceous plants growing in its shade, mixed with a little earthy matter, the layers of coarse coal. The condition of the durable outer bark of erect trees concurs with the chemical theory of coal, in showing the especial suitableness of this kind of tissue for the production of the purer compact coals. It is also probable that the comparative impermeability of the bark to mineral infiltration is of importance in this respect, enabling this material to remain unaffected by causes which have filled those layers, consisting of herbaceous materials and decayed wood, with pyrites and other mineral substances."

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* "Vegetable Structures in Coal," "Journal of Geological Society," "Conditions of Accumulation of Coal," ibid., xxii., 95. XV., 626. Acadian Geology," 197, 464.

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We need not go far in search of the use vegetation, when we consider the fact that civilised nations are dependent on it for their out the coal of the Carboniferous period and which is one of the secondary consequence cumulation, just as bog-ores of iron occur in of modern peats, it would have been impossi sustain great nations in comfort in the colder the northern hemisphere or to carry on ou manufactures. The coal-formation yields to ian alone about one hundred and sixty mil coal annually, and the miners of the United tract mainly from the same formation nearly million tons, while the British colonies and cies produce about five million tons; and markable fact that it is to the English rac greatest supply of this buried power and heat has been given.

The great forests of the coal period, while the atmosphere of its excess of unwholesome acid, were storing up the light and heat of summers in a form in which they could be recove human age, so that, independently of their us animals which were their contemporaries, they pensable to the existence of civilised man.

Nor can we hope soon to be able to dispense services of this accumulated store of fuel. T of to-day are altogether insufficient for the supp wants, and though we are beginning to apply wa to the production of electricity, and though som ing plans have been devised for the utilisatio direct heat and light of the sun, we are still qu pendent as any of our predecessors on what has b for us in the Paleozoic age.

In the previous pages I have said little respec physical geography of the Carboniferous age; but

be inferred from the vegetation, this in the northern hemisphere presented a greater expanse of swampy flats little elevated above the sea than we find in any other period. As to the southern hemisphere, less is known, but the conditions of vegetation would seem to have been essentially the same.

Taking the southern hemisphere as a whole, I have not seen any evidence of a Lower Devonian or Upper Silurian flora; but in South Africa and Australia there are remains of Upper Devonian or Lower Carboniferous plants. These were succeeded by a remarkable Upper Carboniferous or Permian group, which spread itself all over India, Australia, and South Africa,* and contains some forms (Vertebraria, Phyllotheca, Glossopteris, &c.) not found in rocks of similar age in the northern hemisphere, so that, if the age of these beds has been correctly determined, the southern hemisphere was in advance in relation to some genera of plants. This, however, is to be expected when we consider that the Triassic and Jurassic flora of the north contains or consists of intruders from more southern sites. These beds are succeeded in India by others holding cycads, &c., of Upper Jurassic or Lower Cretaceous types (Rajmahal and Jabalpur groups).

Blanford has shown that there is a very great similarity in this series all over the Australian and Indian region.† Hartt and Darby have in like manner distinguished Devonian and Carboniferous forms in Brazil akin to those of the northern hemisphere. Thus the southern hemisphere would seem to have kept pace with the northern, and according to Blanford there is evidence there of cold conditions in the Permian, separating the Paleozoic

* Wyley, "Journal Geol. Society," vol. xxiii., p. 172; Daintree, ibid., vol. xxviii.; also Clarke and McCoy.

"Journal Geol. Society," vol. xxxi.

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