BITUMINOUS AND ANTHRACITIC. 455 



The Stigmaria presented in its structure, according to Lindley 

 and Hutton, a low, dome-shaped, fleshy trunk, or centre, from the 

 edge of which there radiated a number of horizontal branches, 

 supphed with a multitude of slender, cylindrical, and exceedingly 

 long leaves. The fire-clay, or Stigmaria clay, as we may indif- 

 ferently call it, abounds in these delicate leaves, in a flattened and 

 distorted condition ; and it is partly to them and partly to the com- 

 minuted state of the argillaceous material itself, that the stratum 

 owes its characteristic tendency to crumble in every direction. 

 The branches of the Stigmaria, which usually lie parallel to the 

 plane of the stratum, and are most abundant nearest the coal, 

 it has been suggested, were hollow cylinders, composed entirely 

 of spiral vessels, and contained a thick pith. The plants, ac- 

 cording to Dr. Buckland, probably floated on the water. 



Of the Roof of the Coal. 



If we examine, in the next place, the strata which immediately 

 rest upon the coal, we shall discover a condition of things in 

 striking contrast with the phenomena of the under-clay. Instead 



do not rest upon it, as the Sections will show." And ag-ain. " From the circumstance, 

 that so many cases occur, where a tolerably pure fire-clay lies immediately under, and in 

 contact with, a bed of coal, it may be inferred, that such clay stratum could not have been 

 the soil, where g-rew the vegetable matter which produced the coal, unless this vegetable 

 matter was a moss, a peat, or some aquatic plant ; because, in the clay, there is no ap- 

 pearance of trunks, or other vegetable impressions, beyond slender leaves, as of a long 

 grass." 



" The fact, that particular strata accompany the main coal for many square miles, would 

 support the idea, that an immense flat was originally covered with the substance of this 

 fire-clay, many feet thick, and that, upon this flat, there took place an uniform growth of 

 a distinct single vegetation, which must have occupied the position for a long period, and 

 thus furnished the substance which composes the main coal. The alternations of fire- 

 clay and coal-seams would favor the notion, that these materials were originally mixed 

 together in a fluid, and that those of the former, by their gravity, would first subside, whilst 

 the vegetable matter, or those of the latter, would undergo a more gradual deposition. 

 Hence, by a repetition of the process, the alternations of the strata would be produced. 

 Besides, it may be supposed, that if the strata of coal have derived their origin from the 

 growth and destruction of a forest, some portions of them would have been thicker than 

 others, and ahered in quality, or have retained, at least, some traces of forest trees ; 

 whereas, on the contrary, most extraordinary uniformity in quality, compactness, and 

 thickness of the seams, prevails to a great extent."* 



* Geologicd] Facts, hy Edward Mnmmfltt.p. 73. 



