THE CARBONIFEROUS AGE. 119 



charcoal. Thin partings of dark shale also occur, 

 and these usually present marks and impressions of 

 the stems and leaves of plants. Above the coal is 

 its " roof " of hardened clay or sandstone, and this 

 generally holds great quantities of remains of plants, 

 and sometimes large stumps of trees with their bark 

 converted into coal, and the hollow once occupied 

 with wood filled with sandstone, while their roots 

 spread over the surface of the coal. Such fossil 

 forests of erect stumps are also found at various 

 levels in the coal measures, resting directly on under- 

 clays without any coals. A bed of coal would thus 

 appear to be a fossil bog or swamp. 



This much being premised about the general nature 

 of the sooty blocks which fill our coal-scuttles, we 

 may now transport ourselves into the forests and 

 bogs of the coal formation, and make acquaintance 

 with this old vegetation, while it still waved its 

 foliage in the breeze and drank in the sunshine and 

 showers. We are in the midst of one of those great 

 low plains formed by the elevation of the former 

 sea bed. The sun pours down its fervent rays upon 

 us, and the atmosphere, being loaded with vapour, 

 and probably more rich in carbonic acid than that 

 of the present world, the heat is as it were accu- 

 mulated and kept near the surface, producing a 

 close and stifling atmosphere like that of a tropical 

 swamp. This damp and oppressive air is, however, 

 most favourable to the growth of the strange and 

 grotesque trees which tower over our heads, and 



