20 INTRODUCTION. 



tion the loss of organic compounds necessarily connected with the process of 

 carbonisation. Again, such powerful streams, as would be required to 

 transport the whole of the materials which formed our seams of coal, must 

 have been too turbulent to have been favourable to the preservation of 

 vegetable remains. But we find all the impressions of the plants regularly 

 spread out on the planes of stratification in the thin slates of the clay-beds, 

 which so often occur in the roof of the seams. The most delicate fern- 

 leaves are beautifully preserved, showing their pinnae in the normal position 

 and never twisted about by the eddies of a stream. All these circumstances 

 are in favour of the view, that the slaty beds also which form the roof of the 

 coal-seams were deposited with a quietness which excludes the action of a 

 strong current. 



Unger 1 also is a decided supporter of the autochthony of the beds of 

 coal, but he is at the same time convinced that the bogs of the period of 

 the Coal-measures could not have answered properly to our recent peat- 

 bogs, and has distinctly expressed this opinion. He shows quite con- 

 vincingly 2 that we must on no account imagine that they resembled the 

 peat-bogs of our mountain districts, for a uniform tropical temperature 

 prevailed over the whole surface of the earth during the formation of the 

 coal-scams, and such a temperature would appear to be incompatible with 

 the existence of upland peat-bogs. This is doubtless true ; there are no 

 beds of Sphagnum in the tropics, or they form only here and there on the 

 highest mountains ; and that a uniform temperature prevailed over the 

 whole earth in the time of the Coal-measures is certain from the fact, that 

 in deposits of that era from north polar regions to Australia assemblages 

 of plants essentially similar if not identical are found everywhere as 

 constituents of the coal. On this point the reader may consult Carru- 

 thers 3 for Brasil and also for Queensland 4 , O. Feistmantel 5 and Mac Coy 6 

 for Australia, Dawson 7 for Canada and New Brunswick, Heer 8 for Polar 

 lands, Schenk 9 for China, Zeiller 10 for the Zambesi country, Grey 11 for 

 Cape-colony. Unger evidently knew of but one analogous case to which 

 he could appeal in the tropical zone, namely that of the floating islands in 

 the lake of Tagua in Bengal which are covered with trees and shrubs. Had 

 he been better acquainted with the Great Dismal Swamp, he would 

 certainly have noticed it, for it would have answered in all essential points 

 to his idea of the swamps of the Coal-measures. Goppert 12 had meanwhile 

 become acquainted with Lyell's communications on the subject, and has 

 quoted them in the preface to his work as an adequate representation of his 

 idea of the bogs of the Carboniferous period. 



1 Unger (6). " Unger (6), p. 135. 3 Carrathers (7). 4 Carruthers (10). 



8 O. Feistmantel (1), iii. 6 Mac Coy (1). 7 Dawson (8). * Heer (5). Schenk (2). 

 lv Zeiller (13). li Grey (1). Goppert (14). 



