404 VEGETATION OF THE CARBONIFEROUS PERIOD 



elusion that Sigittarice are the trunks of those tree-ferns, a subject 

 to which I shall revert at a future part of this essay. A third and the 

 only other explanation that I can propose is, that the roots were planted 

 in the peat, and with that are now turned to coal, thus being as effectu- 

 ally obliterated as are the roots of those numerous upright stumps 

 of Sigillarice which I consider to have undoubtedly grown on the surface 

 of the coal, and spread their roots into, or along the surface of its mass. 



No fewer than one hundred and forty species of ferns are enumerated 

 as having inhabited those few isolated areae in England over which the 

 coal has been worked, at the time when the latter was formed. This 

 is a strange contrast to our existing Flora, which boasts but 50 species 

 of that order, upon a surface of incomparably greater extent than what 

 we have examined of the carboniferous period. It is, indeed, doubtful 

 whether all the fronds now in Great Britain would equal in number 

 those contained in the largest seams ; so that under whatever light the 

 predominance of the ferns be regarded, whether in amount of species or 

 specimens, they indicate a climate far different from the present. I 

 have before said, that it is only in the tropics, and in the equable, moist, 

 higher latitudes of the southern hemisphere, that any remarkable 

 luxuriance of ferns is met with. A climate warmer than ours now is 

 would probably be indicated by the presence of an increased number 

 of flowering plants, which would doubtless have been fossilized with 

 the ferns ; whilst a lower temperature, equal to the mean of the seasons 

 now prevailing, would assimilate our climate to that of such cooler 

 countries as are characterized by a disproportionate amount of ferns. 

 This then is an argument unfavourable to the theory of central heat 

 having warmed the surface, or of the direction of the poles being so 

 altered as to have exposed Great Britain to a tropical climate, and 

 demanding only a different disposition, and perhaps proportion of land 

 and water to that now existing ; judging from the southern hemisphere, 

 where it is seen that the relative proportions of land and water modify 

 the Flora most materially. 



With regard to the distribution of these fossil ferns out of Britain, it 

 appears that their ranges were as wide as are those of the present day ; 

 perhaps more so, when we consider how extremely difficult is the deter- 

 mination, and no less the identification of the species and specimens, 

 and that the general tendency is probably to the multiplication of 

 species. Of the British species, about 50 are known to occur in the 

 coal-beds of North America, some of them ranging there from the 

 latitude of Nova Scotia to 35° S., and abounding in these and various 

 other intermediate coal-fields. On the continent of Europe again there 

 are about as many of the British species. 



Again, turning to the living ferns, we find that of the 50 inhabiting 



