178 On the Formation of Coal. 



four times as many species of flowering plants as New 

 Zealand, whose total length is 900 miles. Yet in the latter 

 Dr Hooker has collected as many as 36 kinds of fern in an 

 area not exceeding a few acres, to whose vegetation, which 

 presented scarcely a dozen flowering plants and trees be- 

 sides, they gave a most luxuriant aspect. An equal area 

 in the neigbourhood of Sydney, in about the same latitude, 

 would have yielded upwards of an hundred flowering plants 

 and but two or three ferns. New Zealand possesses more than 

 four times as many ferns as Tasmania, and the same species 

 that are found at its southern extremity, prevail also at the 

 northern, and extend even to the Society and Sandwich 

 Islands. On the other hand, the campos of Brazil, the sandy 

 flats of Southern Africa, and th^ similar plains of Australia, 

 though apparently sterile, yet abound in flowering plants, but 

 unaccompanied with ferns. Hence the abundant remains of 

 the latter in the coal formation, seem to prove that the climate 

 then was temperate, equable, and humid, and the land covered 

 with a dense vegetation, uniform in aspect and distinguished 

 by its general poverty in varied forms. In the coal formation 

 of Great Britain no fewer than 140 species of fossil ferns 

 have been enumerated, whereas in its present flora only fifty 

 are known to exist, and it is doubtful whether all the fronds 

 or fern leaves now in Great Britain would equal in number 

 those contained in the largest seams of coal. Such a predo- 

 minance of ferns is only found in the tropics, or in the equable 

 moist climates of the southern hemisphere. Had the climate 

 of Britain, either from the escape of central heat, or an alter- 

 ation in the position of the poles, resembled that of the tropics, 

 it seems probable that the number of flowering plants fossil- 

 ised with the ferns would have been increased ; and hence 

 the supposition is more probable that this character of the 

 vegetation rather arose from the more uniform nature of the 

 seasons, with no increase of mean temperature. And this 

 uniform temperature seems to have prevailed over the whole 

 northern hemisphere, as of the British coal ferns about fifty 

 are found in the carboniferous beds of North America, and 

 as many in those of the continent of Europe. 



