476 



JOURNAL OP HOBTICULTURE AND COTTAGE GARDENEB. 



( Jaae 36, I860. 



of temperature would to a greater or less extent disappear. 

 Now geological facts indicate that in the coal period the greater 

 portion of the earth's surface was covered with water, and that 

 the land which did exist was low and marshy. 



The key to unlock the mystery of the existence in high lati- 

 tudes of the heat requisite to the growth of the coal plants 

 eeems to me to be found in this circumstance : The immense 

 mass of water composing the almost universal ocean, was 

 doubtless traversed in all parts by currents similar to the Gulf 

 Stream, but on a still more magnificent scale — and these it 

 was which enabled the coal plants to flourish so near the pole. 

 I have said nothing of the possibility of the crust of the earth 

 having been warmed by the inner fires. This may have con- 

 tributed somewhat to the growth of the coal flora, but how 

 much, if at all, seems impossible to be judged. 



The problem, how the plants received their supply of light, 

 is not so easily solved. It is, however, by no means settled 

 how far plants can endure the absence of light. According to 

 Professor Lyell, Palms flourish under glass in St. Petersburgh, 

 lat. ay N., where the shortest days are only five hours long, 

 and seem scarcely more than a glimmering twilight. How 

 much greater departure from their normal supply of light 

 these plants would endure is not known ; but this fact cer- 

 tainly shows that they will bear much greater vicissitudes of 

 light than of heat. Further, many of the living congeners of 

 the carboniferous flora, flourish in the darkest recesses of tro- 

 pical prima?val forests, where no sunbeam ever pierces through 

 the thick foliage, but where a shadowy twihght is alone filtered 

 through the dark screen of living green. If Palms, used to 

 the burning sun of the desert, flourish in lat. 65° N., how much 

 further north can tree Ferns, Club Mosses, &c., native deni- 

 Eens of gloom, exist ? And is it not possible that the ancient 

 flora may have had greater powers of enduring the absence of 

 light than the modern allied families ? 



!i But there was undoubtedly more light in those northern lati- 

 tudes formerly than at present. What is coal but carbon ? and 

 these mUhons of tons of carbon have come from plants which 

 must have obtained them directly or indirectly from the atmo- 

 sphere. Carbon can exist in the air only as carbonic acid. 

 Therefore the atmosphere must have been in that ancient time 

 very largely composed of that gas. Although this gas is so de- 

 structive to animals, yet it is a powerful stimulant to vegetation, 

 and its superabundance must have been a great cause of the 

 wondrous, luxuriant profusion of the carboniferous flora. 



We know that, owing to the refraction of the atmosphere, the 

 etm is seen by us when actually several degrees below the 

 horizon. Now the refracting power of carbonic acid far exceeds 

 that of either nitrogen and oxygen singly or associated. In a 

 latitude where the sun revolves for days a few degrees below 

 the horizon, it is vei-y evident what an effect this great refract- 

 ing power must have had on the length of the days and nights. 

 What a very prolonged twilight must have existed there. Taking 

 into consideration these two thoughts — the small supply of light 

 actually necessary to the growth of some plants, and the pro- 

 longed twilights produced by the high refracting power of the 

 carbonised atmosphere, is it necessary to imagine that the 

 world has turned a somersault, in order to account for the coal 

 teds of Melville Island ? 



Although the ocean covered so much of the earth's surface 

 during the carboniferous era, yet coal is not an oceanic de- 

 posit. No marine remains are found in it either vegetable or 

 animal. The plants out of which coal is formed must have 

 contained a large proportion of lignin or woody fibre to have 

 yielded so much solid carbon. Now, seaweeds have singularly 

 little of this in them. They are mere pulpy, fleshy masses, 

 which, when dried, are but the shadow of their former selves. 

 On the other hand, the coal could not have been produced in 

 a veij dry atmosphere, for the Euphorbias, Cacti, <tc., which 

 flourish on dry inland table-lands, are succulent, fleshy plants, 

 composed very largely of watery juices, with but veiy little solid 

 permanent tissue. Again, when plants die and fall to the 

 ground in an ordinary forest they gi-adually decay until all that 

 remains of them is a black rich mould. Decomposition or 

 decay is nothing but a slow process of combustion ; and, as in 

 that process, if a plentiful supply of air is at hand, continues 

 nntil not only hydrogen, nitrogen, and other unstable elements 

 are hberated, but the very carbon itself oxidised. To obtain 

 the carbon by slow decay, just as to obtain it by rapid decay — 

 i.e., combustion, only enough oxygen must be present to con- 

 Bume the less resisting, more changeable portions of the wood. 

 The only known method by which this can be done on a large 

 BCal? is Nature je tbiough the agency of water, I 



If yon examine a log which has Iain for years at the bottom 

 of a pond, you will find that, although a similar log on the 

 shore would have crumbled in the same period into mould, yet 

 it is hard and resistant, only blackened by the touch of time. 

 The air has been excluded in great measure from it, and the 

 carbon remains untouched. TheiCrcator has given a constita- 

 tion to marsh plants, which peculiarly fits them for the forma- 

 tion of coal. They contain a remarkably large amount of woody 

 fibre. Take the soft pliant sphagnum or bog moss, and delicate 

 as it seems, it actually contains a large proportion of lignin — 

 wiU yield more carbon, pound for pound, than the firm, bard 

 giants of the forest. 



It has been shown that coal has been formed under water, 

 and this peculiar constitution of marsh plants would indicate 

 that it had been formed in hogs or marshes, and not at the 

 deltas of rivers. This is confirmed by many circumstances, 

 among which are these two : — First, the fact that so many 

 stumps and even trunks of trees are found standing in an up- 

 right condition, ajiparently just as they grew ; second, the 

 immense length and breadth of some of the coal fields, coupled 

 with the circumstance of there having been but so little land 

 in those days, seem strongly to oppose the idea of their forma- 

 tion at the mouth of a river. 



It seems certain, upon looking at all sides of the question, 

 that there were immense swamps in the coal ages similar to 

 the famous peat bogs of Ireland and other northern countries, 

 and that it was in them that the depositions of carbon took 

 place. The top of a peat bog is covered over by a luxuriant, 

 living, growing vegetation, whilst underneath is an ever-in- 

 creasing mass of dead, decaying, vegetable matter. The plants 

 which form by far the larger proportion of each of these are 

 the Mosses. 



Upon examining peat taken from near the surface, it will be 

 seen to consist of a matted interwoven mass of stems and roots, 

 blackened by incipient decay, but preserving their form and 

 structure. The further from the stirface the more marked is 

 the effect of the slow combustion, till at last a point is reached 

 where the form of the component plants is lost, and the peat 

 is reduced to a black, carbonaceous, spongy mass. Now this 

 material needs only heat and pressure to form it into coal. It 

 has actually been dug out, dried, exposed to a great pressure 

 and heat, and an artificial coal thus been made. 



As impressions and even parts of individual plants are 

 found scattered through the coal, so even in the fully-formed 

 peat portions of many species of plants exist. The Moss, 

 however, never retains its structure or form, but is converted 

 into the black, uniform, carbonaceous mass, which constitutes 

 by far the greater part of the peat. No traces of Mosses have 

 as yet been found in the coal. Does it follow from this that 

 they did not exist in the carboniferous era ? Much of the 

 coal when examined by the microscope does not exhibit any 

 definite structure ; and is it not very probable that it corre- 

 sponds to the stractureless portion of the peat in origin as 

 well as constitution, and that Mosses flourished abundantly 

 iu that ancient flora ? 



The plants that have written their history most profusely on 

 the coal and surrounding shales are the Ferns. Everywhere 

 are their traces visible. Sometimes a single frond, nicely 

 smoothed out as though pressed for an herbarium ; again, great 

 piles of them, the fronds crossing, recrossing, and interming- 

 ling with one another in endless confusion. Although, as has 

 just been indicated, the abundance of structural reliqiur is an 

 index rather of the indestructibility of the plant than its pris- 

 tine profusion, yet it cannot be doubted that the Filices held a 

 very prominent place in the coal flora : their appearance 

 must have been very similar to the tropical Ferns of the 

 present day. There are found imbedded in the coal huge 

 truuks which have their surface fretted with verj- large, more 

 or less semi-lunar scars. By means of the microscope, Messrs. 

 Lindley and Button have been enabled to demonstrate that 

 these were the trimks of immense tree Ferns. The ordinary 

 frondose Ferns were apparently much the more abundant then, 

 as now. 



Mr. Corda, some years since, described some peculiar TcUqxue, 

 which he called Psaronins. These are very abundant in some 

 localities ; they are always in the form of a short thick stump, 

 with a tliick hard bark, whose surface is covered with a dense 

 mass of rootlets. These, according to Professor Lesquereux 

 resemble, both in external form and internal structure, the 

 short rootstocks of some of the immense Ferns of the island 

 of Java. 



The study of fossil Ferns is environed with almost inenr- 



