82 M. Brongniart on the different Floras which 



Lastly, we are not sufficiently acquainted with the influence 

 of the nature of the atmosphere upon the life of vegetables, when 

 prolonged throughout their entire existence, to know whether 

 important differences in the composition of that atmosphere, 

 and above all the (very probable) presence of a greater propor- 

 tion of carbonic acid, might not favour the existence of certain 

 classes of the vegetable kingdom and oppose that of other 

 groups. 



I will terminate this sketch of the vegetation of the carboni- 

 ferous period, by directing attention to the facts that the coal 

 formation, which, almost solely, contains the remains of it, is 

 evidently a terrestrial and freshwater formation ; that the layers 

 of coal which it contains are the result of the accumulation in 

 situ of the remains of the plants, which covered the soil in the 

 same manner as the layers of peat or the vegetable mould of 

 great forests ; that it is only in certain exceptional circumstances 

 that these layers alternate with layers containing the remains of 

 marine animals, and can be considered as the result of the trans- 

 port in the sea of the terrestrial plants which occur in them. 



This vegetation of the great carboniferous period disappeared 

 almost completely with it ; the Permian period which succeeded 

 presents only a kind of residue already deprived of the majority 

 of its most characteristic genera; and during theVosgesian period, 

 or that of the gres bigarrCj we find no longer any trace of it. 



I cannot close this account of the vegetation of the carboni- 

 ferous period without saying a few words on the incompre- 

 hensible exception to this regular and uniform distribution of 

 fossil vegetables which would be afforded by the anthracitic for- 

 mations of the Alps, if they belonged really to the epoch of the 

 lias, as held by M. Elie de Beaumont and several other distin- 

 guished geologists who adopt his opinion. I cannot discuss 

 here the reasons, derived from geological observations properly 

 so called, which have led M. de Beaumont to this conclusion ; I 

 am aware of all the weight which the so accurate and well- 

 directed observations of my learned friend possess in science ; 

 but when we see that the researches which so many scientific 

 men and collectors have made, have shown that the plants con- 

 tained in these strata are without exception those of the coal 

 period, without the intermixture of a single fragment of the 

 fossil plants of the lias, of the Jurassic epoch, of the keuper, or 

 of the gres higarre^ we seek in vain for an explanation of this un- 

 paralleled fact, and ask whether the few shells which have chiefly 

 contributed to cause the reference of these formations to the Ju- 

 rassic period, are a very positive proof of this geological position. 

 Their small number, their state of preservation so imperfect that 

 their specific determination is impossible or very doubtful, do 



