88 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 3, 



is very striking. The absolute identity of some species is not per- 

 haps so remarkable as the very great general similarity of the whole ; 

 for those among the Frostburg plants, which cannot be satisfactorily 

 identified with British species, are in every instance very closely 

 allied to them. We should not find so great a degree of resemblance 

 on comparing the recent floras of two regions separated by so many 

 degrees of latitude, whether in Europe or North America. If we 

 may reason at all as to climate from the fossil vegetation of a 

 country, we must suppose that the climate varied less rapidly with 

 the latitude than it does at present. 



I must not omit to take notice of the opinion maintained by Pro- 

 fessor Lindley*, " That the numerical proportion of different fami- 

 lies of plants found in a fossil state throws no light whatever upon 

 the ancient climate of the earth, but depends entirely on the power 

 which particular families may possess, by virtue of the organization 

 of their cuticle, of resisting the action of the water wherein they 

 floated previously to their being finally fixed in the rocks in which 

 they are now found." To this conclusion it appears to me that there 

 are strong objections. It seems to have been deduced by Professor 

 Lindley from the results of an experiment (recorded in the third 

 volume of the ' Fossil Flora') on the comparative durability of va- 

 rious plants when immersed in water. In the first place, as M. 

 Adolphe Brongniart has already remarked, Dr. Lindley 's theory 

 does not at all explain why the proportional number of ferns should 

 be greater in the coal formation than in any subsequent deposit, nor 

 why the leaves of dicotyledonous plants, which are almost, if not 

 entirely wanting in that formation, should be so abundant and so 

 well-preserved in the freshwater deposits of the tertiary period. If 

 maceration in water destroyed them in the one case, it would surely 

 have done so in the other. Moreover, Dr. Lindley's experiment, 

 however ingeniously devised and carefully conducted, does not sup- 

 ply all the data necessary for deciding the question ; nor are its re- 

 sults altogether in accordance with the phaenomena we observe in 

 the carboniferous strata. The species of ferns submitted to experi- 

 ment by him were only six in numberf, — too few, I think, to justify 

 us in concluding that the plants of that tribe generally possess in an 

 eminent degree the power of resisting maceration in water. In this 

 number were not included any of the more tender and delicate kinds 

 of ferns, such as those HymenophyllecB, which are almost compara- 

 ble to mosses in the filmy, delicate and fragile texture of their leaves, 

 and of which many representatives are found in a fossil state. It is 

 difficult to believe, without more positive proof, that fronds so thin 

 and membranous as those of several species of Sphenopteris which 

 occur in the coal formation, could have endured long maceration in 

 water, when we learn from Dr. Lindley's experiment that even that 

 singularly hard ajid rigid plant the Equisetum hijemale, of which the 

 stems are coated with silex, perishes within two years under this 

 process. 



Again, Dr. Lindley concluded from his experiment that the fruc- 

 * Fossil Flora, vol, iii. p. 12, f Ibid. p. 5. 



