80 PICTURESQUE SKETCHES 



the existence of extraordinary means to produce that 

 change. Nothing, however, is more certain than that 

 all coal was once vegetable ; for in most cases woody 

 structure may be detected under the microscope, and 

 this, if not in the coal in its ordinary state, at least in 

 the burnt ashes which remain after it has been ex- 

 posed to the action of heat, and has lost its bitumi- 

 nous and semi-crystalline character. This has been 

 too well and too frequently proved by actual experi- 

 ment, to require more than the mere statement of the 

 fact. 



The principal vegetable remains, the study of which 

 conducts the botanical fossilist to a knowledge of the 

 trees and 'shrubs that clothed the land during this 

 period, are not met with in the substance of the coal 

 itself, but in the shales and sandstones so abundantly 

 mixed with the coal. These beds have received, and 

 occasionally retained, the fragments that have been 

 deposited in them ; and from such fragments, consist- 

 ing of leaves and small branches, portions of the larger 

 branches, or even the entire trunk, and occasionally, 

 also, internal casts or markings of the surface of the 

 fruits of various trees, conclusions have been arrived 

 at and analogies drawn expressing the relation they 

 bear to existing plants. Now if, in all cases, the solid 

 substance of the trunks and the perfect outline of the 

 leaves and fruits had been preserved, the botanist 

 might fairly have been expected to explain the general 

 character of the vegetation thus exemplified ; but un- 

 fortunately this is not the case. In most instances, 

 even those which seem most favourable, it is only the 

 cast of the tree in sandstone, the impression made by 

 the outside or inside of the bark, and a little of the 



