TUE CARBONIFEROUS AGE. 141 



them an iutroduction to tlie next group of creatures 

 we have to consider. In the coal formation in all 

 parts of the world it is not unusual, as stated already 

 in a previous page, to find erect trees or stumps 

 of trees, usually Sigillarige, standing where they grew ; 

 and where the beds are exposed in coast cliffs, or road 

 cuttings, or mines, these fossil trees can be extracted 

 from the matrix and examined. They usually consist 

 of an outer cylinder of coal representing the outer 

 bark, while the space within, once occupied by the 

 inner bark and wood, is filled with sandstone, some- 

 times roughly arranged in layers, the lowest of which 

 is usually mixed with coaly matter or mineral charcoal 

 derived from the fallen remains of the decayed wood, 

 a kind of deposit which afibrds to the fossil botanist 

 one of the best modes of investigating the tissues of 

 these trees. These fossil stumps are not uncommon in 

 the roofs of the coal-seams. In some places they are 

 known to the miners as " coal pipes," and are dreaded 

 by them in consequence of the accidents which occur 

 from their suddenly falling after the coal which sup- 

 ported them has been removed. An old friend and 

 helper of mine in Carboniferous explorations had a 

 lively remembrance of the fact that one of these old 

 trees, falling into the mine in which he was working, 

 had crushed his leg and given him a limp for life ; and 

 if he had been a few inches nearer to it would have 

 broken his back. 



The manner in which such trees become fossilized 

 may be explained as follows : — Imagine a forest of 



