296 



♦ KNO\VLEDGE ♦ 



[Oct. 10, 1884 



the carboniferous group is the coal-group far excellence ; 

 and when to this consideration is added the enormous 

 thickness of the series of strata included in this group, 

 we seem justified in concluding that this long period 

 was characterised by some remarkable and distinctive 

 peculiarity. 



Now, whether we consider the lower portion of 

 the carboniferous series remarkable for the masses of 

 limestone derived chiefly from animal substances, or 

 the upper, where the coal - seams or vegetable layers 

 abound, we find evidences of the presence of enormous 

 quantities of carbon. In the upper part, the mere exist- 

 ence of a most abundant vegetation implies the presence of 

 vast quantities of carbonic acid gas in the air. It seems 

 not unlikely that this gas escaped from subterranean regions 

 through the outlets formed by volcanoes ; and the idea is 

 suggested that the carboniferous period was one of great 

 volcanic energy. In the older periods, there was probably 

 a greater degree of subterranean activity, and from the 

 carboniferous period onwards, even until our own, move- 

 ments of the earth's crust have been probably more irre- 

 gular and violent. But it would seem likely that, in the 

 carboniferous period, an intermediate state of things pre- 

 vailed when, owing to the greater heat of the earth's crust, 

 and consequently the greater relative thickness of the 

 plastic subterranean portions of the crust, the movements 

 were more steady, and aflected wider regions than at pre- 

 sent, while the relief given by volcanic craters, instead of 

 being intermittent as at present, was aflibrded uniformly 

 and on a grander scale. 



If this were, indeed, the case, then, towards the close of 

 the carboniferous period, great disturbances of the earth's 

 crust might be expected to have taken place, since that 

 would be the time when the chief volcanic vents ceased to 

 relieve the pent up subterranean forces. This accords well 

 with the condition of the geological record. " The termi- 

 nation of the carboniferous formation," says the author of 

 the " Vestiges of Creation," " is marked by symptoms of 

 volcanic violence" (by which he evidently means simply 

 subterranean violence), " which some geologists have con- 

 sidered to denote the close of one system of things and the 

 beginning of another. Coal-beds generally lie in basins, as 

 if following the curve of the bottom of the seas ; but 

 there is no such basin which is not broken up into pieces, 

 some of which have been tossed up on edge, others 

 allowed to sink, causing the ends of strata to be, in 

 some instances, many yards, and, in a few, several 

 hundred feet, removed from the corresponding ends of 

 neighbouring fragments. These are held to be results of 

 volcanic movements below, the operation of which is 

 further seen in numerous upbursts and intrusions of fire- 

 born rock (trap). That these disturbances took place 

 about the close of the formation, and not later, is shown 

 by the fact of the next higher group of strata being com- 

 paratively undisturbed. Other symptoms of this time of 

 violence are seen in the beds of conglomerate which occur 

 among the first strata above the coal. These, as usual, 

 consist of fragments of the elder rocks, more or 

 less worn from being tumbled about in agitated water, 

 and laid down in a mud paste, afterwards hardened.* It is 



* "Volcanic disturbances," adds our author in a note, "break 

 up the rocks ; the pieces are worn in seams, and a deposit of con- 

 glomerate is the consequence. Of porphyry there are some such 

 pieces in the conglomerate of Devousliire, three or four tons in 

 weight." It is evident from this note, following, as it does, on the 

 above passage as to the older rocks, that the vrriter is speaking of 

 subterranean disturbances, not volcanic action, properly so-called; 

 for volcanic action does not break up the older rocks ; that is the 

 work of earthquakes. 



to be admitted for strict truth " (rather a desirable object, 

 by the way, in all such inquiries) " that, in some parts of 

 Europe, the carboniferous formation is followed by superior 

 deposits, without the appearance of such disturVjances be- 

 tween their respective periods ; but apparently this case Ls 

 exceptional. That disturbance was general is supported by 

 the further and important fact of the destruction of many 

 forms of organic being previously flourishing, particularly 

 of the vegetable kingdom." 



It may be remarked in passing that the coal-seams are 

 strikingly deficient in the fossil remains of animals. It is 

 natural to ask, says Sir Charles Lyell, whether there were 

 not air-breathing inhabitants of those forest regions where 

 the accumulations of vegetable matter produced the coal- 

 beds ; but, if abundance of carbonic acid gas in the air 

 were a main condition of the great vegetable wealth of the 

 carboniferous period, the probability would seem to be that 

 air-breathing creatures would be few, and those few of the 

 lower orders of animal life. Certain it is that the poverty 

 of the coal-seams in remains of animals has long been com- 

 mented upon by geologists. We find footprints of a 

 monstrous newt, or rather of an animal resembling 

 the tadpole of the newt* These creatures were truly 

 amphibious, however, sharing the dominion of the water 

 with the ganoid fishes — an association wliich " reminds 

 us," says Lyell, " that the living " creatures of the same 

 order " in America frequent the same rivers as the ganoids, 

 the bony pike?." They were undoubtedly powerful swim- 

 mers, Professor Huxley considers ; and, indeed, the main 

 evidence we have of their having been air-breathers is the 

 circumstance that they left footprints on the sand. If they 

 had been walking under water, their weights would have 

 been so much reduced that they would have left no im- 

 pressions, or only faint ones, whereas these are deep and 

 distinct. They are not unlike the impressions which would 

 be left by a small and rather plump hand. It is by no 

 means clear that this creature ever made its way into the 

 ancient forests, or could be in any proper sense regarded as 

 their inhabitant, t 



I have mentioned impressions left in sand belong- 

 ing to the carboniferous period, and the ingenious way 

 in which geologists have explained the features of these 

 impressions. There is, however, a record on the sand- 

 stone of this period, which is, perhaps, even more 

 significant. Impressions of rain-drops have been de- 

 tected in carboniferous sandstone by Dr. Dawson, Sir 

 Charles Lyell, and, more recently, by Mr. Brown, in 

 Australia ; and these rain-marks are, on the average, 

 about as large as those which are produced by the rain 

 of our own period. As Lyell well remarks, "the great 

 humidity of the climate of the coal period had been 



* The reader will be reminded of the suggestive remarks, by the 

 author of the " Vestiges of Creation," on similar tracks left by the 

 Xahyri-nUxoAont ol Owen: "That massive batrachian which leaves 

 its handlike footsteps in the new red sandstone, and then is seen 

 no more. Not for nothing is it that we start at the picture of that 

 strange impression — ghost of anticipated humanity — for apparently 

 it really is so." It need hardly be said, however, that this is no* 

 the view at present entertained by naturalists. 



t Owing to the circumstance that in our books on geology this 

 creature is called a batrachian, many popular writers have been 

 led to assert that a monstrous frog inhabited the ancient forests 

 whence the vegetation of the coal-seams was derived. But the 

 order of batrachians includes other animals than the frog and toad. 

 According to the views at present adopted of the batrachian of 

 the carboniferous period (as well as of a kindred bnt later species 

 called by Professor Owen the labyrinthodont), this creature was 

 further removed even than the newt from the common frog. It 

 probably resembled in structure creatures still existing (but on a 

 much smaller scale), which have four limbs like the newt, but have 

 gills as well as lungs. 



