194 



FORMATION OF COAL. 



age ? I must ask you in imagination to descend a coal mine with 

 me. Let us select a seam of our own Bristol coalfield, and there 

 see what information we can gather ; but we must remember that 

 every seam varies as to the exact nature of the strata immediately 

 over it. Before us is the coal A Fig i, under it a bed of fireclay, 

 in which we find a peculiar fossil root Stigmariaficoides, associated 

 with small markings which are probably other roots— this is 

 characteristic of seams all over the world. 



Fig. I. 



The Stigmariaficoides is of a cylindrical form enclosed in a black 

 coal-like envelope, the internal structure is seldom well preserved, 

 all that presents itself to the eye is a calcareous mass inside the 

 o rganic cylinder, which represents the woody part of the plant. 

 The external surface is covered with small pits^ from which 

 rootlets were given off. 



We will pass over the coal for the present, and examine next the 

 bed over it. In the case before us it is a black shale four inches 

 thick: in some instances these shales contain a large per centage 

 of hydro-carbon, which have accumulated from the decomposition 

 of the vegetable matter during its transformation into coal : in this 

 fossils are not common. Next is bed d, a moderately hard 

 "duns" in which are found reed-like fossils, termed by the miners 

 '-' flags," but they appear to me to be the genus Cordaites, This 

 fossil has a great resemblance to a reed, I have found them 



