XIV.] LIVING MATTER AND ITS EFFECTS. 



237 



commonly found in the coal and the shales, and are known 

 as sigillarics (Fig. 67).^ There is consequently no doubt 

 that the stigmaria is nothing but the root of the sigillaria, 

 and that the under-clay represents the soil of an ancient 

 forest in which these and other trees flourished. 



In examining one of these sigillaria-stems, it will pro- 

 bably be found that the bulk of the trunk consists of 

 stony matter, but that this is coated by a thin layer of 



Fl 'i 67. — ^i^iilaria altathed to stigmarian ruots. 



coal which represents the original bark of the tree. Hence, it 

 may be assumed that the old trunk rotted away, leaving 

 a hollow tube of bark which has become transformed into 

 coal. But, although coal may have been produced in this 

 way to a limited extent, it would be rash to conclude 

 that the whole of our coal was formed by such a trans- 

 formation. What kinds of vegetable matter have been 

 concerned in the production of coal cannot be determined 

 without the aid of the microscope. 



On attempting to break a mass of coal, it will generally 

 be found that it splits much more readily in certain 



1 Sigillaria, from Lat. sigillum, a seal ; the leaf scars resembling the 

 impressions of a seal 



