100 CRITIQUES AND ADDRESSES. [v. 



surface, sometimes they are covered up by thousands 

 of feet of rock. But, whatever their present position, 

 there is abundant and conclusive evidence that every 

 under-clay was once a surface soil. Not only do car- 

 bonized root-fibres frequently abound in these under- 

 clays ; but the stools of trees, the trunks of which are 

 broken off and confounded with the bed of coal, have 

 been repeatedly found passing into radiating roots, still 

 embedded in the under-clay. On many parts of the 

 coast of England, what are commonly known as " sub- 

 marine forests" are to be seen at low water. They 

 consist, for the most part, of short stools of oak, beech, 

 and fir trees, still fixed by their long roots in the bed 

 of blue clay in which they originally grew. If one of 

 these submarine forest beds should be gradually depressed 

 and covered up by new deposits, it would present just 

 the same characters as an under-clay of the coal, if the 

 Sigillaria, and Lepidodendron of the ancient world were 

 substituted for the oak, or the beech, of our own times. 



In a tropical forest, at the present day, the trunks of 

 fallen trees, and the stools of such trees as may have 

 been broken by the violence of storms, remain entire for 

 but a short time. Contrary to what might be expected, 

 the dense wood of the tree decays, and suffers from the 

 ravages of insects, more swiftly than the bark. And the 

 traveller, setting his foot on a prostrate trunk, finds that 

 it is a mere shell, which breaks under his weight, and 

 lands his foot amidst the insects, or the reptiles, which 

 have sought food or refuge within. 



The trees of the coal forests present parallel condi- 

 tions. When the fallen trunks which have entered into 

 the composition of the bed of coal are identifiable, they 

 are mere double shells of bark, flattened together in 

 consequence of the destruction of the woody core ; and 

 Sir Charles Lyell and Principal Dawson discovered, in the 



