ON THE ORIGIN OF COAL-FIELDS. 



151 



strictly speaking, therefore, it can only indicate the probable condition of the climate at 

 and near the spots where the fossil plants were detected. 



Lastly, we descend into the ancient carboniferous strata under consideration. Now, 

 as in these the whole fauna and flora are very dissimilar from the animals and plants 

 of the present day, — and even distinct from those of the intermediate periods,, — thus 

 affording evidence of having existed during a very remote sera, — so there are abundant 

 proofs, in the nature of the coal and its associated strata, that the substance there accu- 

 mulated is the result of gradual molecular changes among the elements of organic 

 matter, which have been buried during many ages beneath the increasing and varied 

 sediments. The vegetation of this distant epoch, the earliest, as I shall hereafter show, 

 in which the presence of any considerable quantity of terrestrial plants has been yet de- 

 tected, is said by botanists to bear an exclusively tropical character, or in other words, 

 to prove a moist atmosphere and warm climate ; for the large succulent plants, and 

 arborescent ferns which abound in the coal measures, could only have grown to their 

 vast size with much moisture, and an atmosphere so moist could alone be obtained in a 

 hot climate. Hence, though it is manifest from the evidences adduced, that dry land was 

 in existence in the immediate neighbourhood of the coal-fields described, such land con- 

 sisted probably of nothing more than low insular masses, favouring the production of 

 plants requiring a warm climate. (See the small Map, fig. 2, opposite 1 .) This inference 

 is not, however, intended to lead my readers to imagine, that other and larger conti- 

 nents may not have existed at the very same period. 



Whether, therefore, we begin our examination at the present surface, and descend 

 from the vegetable deposits lodged in lakes and estuaries, through the tertiary and se- 

 condary strata, down to the carboniferous system, or ascend from these old rocks, we 

 meet at successive stages with a regular series of analogous proofs, that vegetables, 

 differing in their forms in each successive cera, were drifted from adjacent preexisting 

 lands, and have invariably been the materials out of which coal has been elaborated. 



I shall revert to this interesting subject of fossil vegetation, when the rocks of the 

 Silurian system have been described. In the mean time, to illustrate these views, I 

 annex two small maps. The uppermost of these represents, on a very reduced scale, 

 the actual proportions of land and water, in a part of the North American continent 

 before alluded to. This map is intended to explain how the drift wood, accumulating 



1 Many remarkable and convincing proofs of the strong analogy and similarity of the fossil flora of the coal- 

 fields to plants of tropical and intertropical characters, will be found in that beautifully illustrated work of my 

 esteemed friend Mr. Witham, of Lartington Hall, Yorkshire. With the assistance of Mr. Nicol, Mr. Witham 

 has developed the vegetable tissue, by slicing and polishing the stone containing the impressions and forms of 

 the plants. Mr. W. Hutton has subsequently shown by a similar process that the vegetable tissue is occasion- 

 ally discernible, even in the most compact cone of the Durham and Northumbrian fields. In some of the old 

 coal-fields, the form of the vegetables is actually apparent in the coal itself. Examples of this have been already 

 mentioned, in ill- consolidated coal at Tasley near Bridgenorth, and at the Brown Clee Hills, and other similar 

 cases will be noted in the Dudley coal-field. 



T 2 



