Jan. 1 6, 1879] 



NATURE 



239 



precisely such as we see when an old post, or the stem of 

 a dead tree, undergoing decay, is breaking up into small 

 cubical or rectangular pieces, and which would float 

 freely upon the surface of an overflowing current of 

 water. 



My present impression is that these charcoal layers 

 have originated in the decay of aged stems, such as have 

 produced the "pot-stones '' and "pot-holes" common in 

 our coal-mines. The wood and the greater portion of 

 the bark would accumulate, in a fragmentary state, 

 within the hollow cylinders of the less easily destroyed 

 bast-layer of the bark of such stems, until some recurring 

 flood converted the damp ground into a temporary shal- 

 low lake, filling all these cylinders with water, when all 

 such fragments would speedily float out, leaving the 

 empty cylinders to be occupied by the sands and clays 

 by which they are almost always permanently filled. 

 The displaced vegetable fragments would swim freely for 

 a time, diffused widely over the surface of the waters, 

 but, as the latter subsided, they would settle down upon 

 the layers of more completely disorganised vegetable 

 soil, which, being already damp and soddened, would be 

 likely to remain undisturbed by the temporary and 

 sluggish currents that would exist where a forest-covered 

 swamp was thus overflowed. 



Prof. Green appears to balance very fairly the respec- 

 tive measures in which reproductive spores and the 

 merely vegetative portions of the Carboniferous plants 

 have contributed their quota to the carbonaceous mass. 

 At the same time, much more work remains to be 

 done before our theories on this subject can be regarded 

 as wholly satisfactory. 



The chief point in Prof. Green' s work which I should 

 be disposed to criticise is his map representing the 

 probable distribution of sea and land during the carboni- 

 ferous age. We are so ignorant of the extent to which 

 denudation has affected vast geographical areas, that all 

 such attempts appear to be inevitably hypothetical. At 

 the same time Prof. Green's reasonings on the subject 

 are extremely plausible and ingenious. 



The third chapter of the volume is devoted to the coal 

 plants -especially to the two types of Calamites and 

 Lepidodendron, with the near relative of the latter, the 

 Sigillaria. Since this portion of the volume is avowedly 

 based upon my own memoirs, criticism of any kind would 

 be out of place here. I would only observe that Prof. Miall 

 appears to have reproduced my notions, be they right or 

 wrong, with great accuracy. I may, however, observe 

 here that one of the points for which I have so long 

 contended, in opposition to my French friends, viz., the 

 close identity of Asterophyllites and Sphenophylla, has 

 just received unanswerable confirmation. Herr von 

 Stur has obtaitied both these types of foliage tipon one 

 single plant, the former being the ordinary vegetative 

 foliage, and the latter the whorls of leaves belonging to 

 the fruiting branches. 



In the fourth chapter we find Prof. Miall upon his own 

 ground. In it he deals with the animals of the coal, 

 measures, to the history of many of which he has made 

 such valuable contributions. The chapter affords a rich 

 illustration of the progress which the animal palaeontology 

 of the coal-measures has made during the last half 

 century. Within that period Dr. Hibbert first called 



attention to the large teeth and bones of the Burdie-house 

 limestone. It was only in the third decade of the century 

 that we began to find scanty fragments of similar objects 

 in the Ardwick limestones of Manchester, and it was at a 

 yet later period that the Wigan Cannel was found to be 

 rich in remains of similar objects. How changed this 

 portion of our knowledge now is the reader of Prof. 

 Miall's interesting chapter will readily learn. Prof. Miall 

 wisely explodes the baseless notion of an atmosphere 

 ladened with a superabundance of carbonic acid — existing 

 during the Carboniferous age — a notion which still reap- 

 pears in some geological works, but which rests upon no 

 probable foundation. On the other hand he very correctly 

 shows the importance of studying the fishes of the Car- 

 boniferous rocks when attempting to classify these rocks 

 by the light of their animal remains. He points out the 

 rarity of the Carboniferous Ganoids in the mountain lime- 

 stone contrasted with the comparative abundance of 

 the Elasmobranchs — a statement which every geologist 

 familiar with these rocks will readily confirm, and he 

 shows also how difficult it is to determine between the 

 several influences of marine and fresh- waters in producing 

 the Carboniferous beds. At the same time, fully admitting 

 the correctness of Prof. Miall's statement that the Ganoids 

 become proportionately more numerous as we ascend 

 from the limestone to the newer beds, the Elasmobranchs 

 in the upper coals of Lancashire and Yorkshire are far 

 more numerous than in any known estuarian or fresh- 

 waters at the present day, and consequently they place a 

 great difficulty in the way of our regarding the upper Car- 

 boniferous, sedimentary deposits as being absolutely due 

 to fresh water. Prof. ^Sliall admits that his conclusions 

 on this point compel us to admit "the supposition that the 

 Elasmobranchs were more largely fluviatile than in any 

 other periods." On the other hand, seeing how largely 

 the noble ganoids of the Permian, Liassic, and Creta- 

 ceous ages were undoubtedly marine, it may be as readily 

 contended that the Carboniferous Ganoids were marine 

 as that their Elasmobranch companions were fresh-water^ 



In the fifth and sixth chapters the chemistry of coal is 

 dealt with. For this portion of the work I presume we 

 are wholly indebted to Prof. Thorpe and his auxiliaries 

 in his Leeds laboratory'. This portion of the work is of 

 high interest. Dr. Thorpe has made numerous new 

 analyses, and amongst other matters he has endeavoured 

 to throw further light upon the question first raised by 

 Prof. Huxley, viz., the true influence of Lycopodeaceous- 

 spores in producing the bituminous portions of the coaL 

 But though Prof. Thorpe's researches into this question 

 are highly interesting, the problem is far from solved ; 

 hence I believe he proposes to carry out a further series 

 of analyses, in the hope of throwing further light upon 

 this obscure but important subject. Space does not 

 admit of my referring to the numerous other chemical 

 aspects of coal which Prof. Thorpe so carefully records. 



The four remaining chapters deal respectively with 

 coal as a source of warmth, a source of power, and with, 

 what is commonly called the coal question ; in the two 

 latter chapters, ground gone over by Prof. Jevons, some 

 years ago, is again traversed by Prof. Marshall. To 

 attempt to criticise these latter chapters would be pre- 

 sumptuous on my part, still I cannot quite accept Prof. 

 Marshall's conclusions that what he calls "physical 



