602 STATE OF THE GLOBE AT THE COAL EPOCH. 



climate of the globe, at the time when the coal fossils grew. Ferns of 

 the present day thrive best in a moist insular climate, and many of them 

 occur in tropical climates. Hence Brongniart conjectures that at the 

 coal epoch the surface of the earth consisted of a series of islands in 

 the midst of a vast ocean, and that the temperature was higher gen- 

 erally than that of the present day. In the forests of these islands lofty 

 Lepidodendrons would occur with their delicate and feathery fronds ; 

 Sigillarias, with their fluted stems and enormous matted roots ; Cala- 

 mites, with their singular branches ; Tree-ferns and Coniferous plants, 

 resembling the Norfolk Island Pine, and towering 100 feet above the 

 rest of the forest. He also thinks that the immense deposits of carbon 

 at that epoch, warrant the conclusion that the air contained a large 

 amount of carbonic acid. These conclusions are, of course, mere hypo- 

 theses. In regard to the temperature, it may be remarked, that there 

 is no evidence from the nature of the flora, of a marked increase of 

 temperature at the coal epoch. In New Zealand, which is in a latitude 

 the same as that of a great part of Europe, a very large proportion 

 of the vegetation consists of Acrogenous plants. Ferns and their 

 allies, in that country, cover immense districts, replacing the grasses 

 of other countries, and giving a marked character to all the open land. 

 Some of the ferns attain a height of 30 or 40 feet, and occur in groups. 

 Hemitelia capensis too, a Tree-fern found at the Cape, was also seen 

 by Gardner, at an elevation of 6000 feet, on the Organ mountains, 

 thus showing a capability of enduring a great range of climate, and 

 warning us against hasty conclusions on the subject of the temperature 

 of the world at the coal epoch. 



Dr. Hooker thinks that the prevalence of ferns may be regarded as 

 a probable evidence of the paucity of other plants, and the general 

 poverty of the whole flora which characterized the formation. He is 

 led to these conclusions from observing the mode in which the ferns 

 in Van Dieman's Land and New Zealand monopolise the soil, choking 

 plants of a larger growth on the one hand, and admitting no under- 

 growth of smaller species on the other. In New Zealand he has col- 

 lected 36 kinds of ferns on an area not exceeding a few acres; they 

 gave a most luxuriant aspect to the vegetation, which presented 

 scarcely a dozen flowering plants and trees besides. 



1186. Some have supposed that the plants of the coal fields have 

 been drifted into basins, others that they grew in the spots where they 

 are now found. Beaumont thinks that all the vegetables which are 

 now converted into coal, grew in swampy islands, covered with a 

 luxuriant vegetation, which accumulated in the manner of peat-bogs; 

 that those islands having sunk beneath the ocean, were there covered with 

 sand, clay, and shells, till they again became dry land, and that this 

 operation was repeated in the formation of each bed of coal. The occur- 

 rence of stems of trees in an erect state (fig. 810), appeared to him to 



