PART II. CHAPTER XXI. 255 



Climate of the Carboniferous Period. 



air from considering the Carboniferous flora. The unquestioned 

 existence of large tree-ferns, such as Caulopteris (Fig. 251.) now 

 exclusively the inhabitants of hot and humid climates, and the 

 great variety of fossil fronds of ferns in the Coal confirm this 

 idea, even if we refuse to accede to the arguments adduced to 

 prove that SigillariaB were tree-ferns of extinct genera. The 

 same views receive farther countenance, if the Lepidodendra and 

 Calamites are rightly conjectured to have been gigantic plants of 

 the orders LycopodiacecB and Equisetacece, which, although 

 most largely developed at present in the tropical zone, are even 

 there of pigmy stature in comparison with the fossil tribes just 

 alluded to. The Araucaria, also, is a family of pines now met 

 with in temperate and warm latitudes ; and the fir trees proper to 

 the forests of arctic regions do not appear to have any fossil re- 

 presentatives in the Coal. M. Ad. Brongniart, when endeavouring 

 to establish the great heat and moisture of the climate of the era 

 under consideration, may perhaps have relied too much on the 

 numerical preponderance of ferns over other orders of coal- 

 plants. We may easily be deceived by such reasoning, because 

 it is founded on negative facts, or the absence of plants of certain 

 orders, families, and genera. On this subject Professor Lindley 

 has observed, that the small variety in the forms of each fossil 

 flora must, in a great degree, depend on the relative, destructi- 

 bility of plants when suspended in water before they are imbedded 

 in strata. In illustration of this point, he threw into a vessel 

 containing fresh water 177 plants, among which were species 

 of all the orders found in the Carboniferous flora, with others 

 representing the remaining families and natural orders in the 

 living creation, and found that, at the end of two years, all had 

 decayed and disappeared except the ferns, palms, Lycopodia- 

 CCCB and Conifertz. The fructification of the ferns had also van- 

 ished, but the form and nervures of the leaves remained.* 



No inference, however, drawn from this experiment, can en- 

 tirety explain away the fact of the vast preponderance in the 

 coal-shales of fern-leaves over those of Dicotyledonous plants. 

 Impressions of these last, together with their wood, are plentifully 

 preserved in tertiary rocks in which fossil ferns are rare ; and 

 had they been drifted down in as large numbers as ferns into the 

 estuaries of the Carboniferous period, they would have left im- 

 pressions of their shape in shale and sandstone, as they have 

 done in more recent formations. 



It would, moreover, be rash to assume that the coal-plants in 

 general floated about in water for a year or two before they were 



* Lindley, FOES. Flora, part 17. 



