BITUMINOUS AND ANTHRACITIC. 



451 



mass, and trace the several divisions, we become impressed with 

 the wonderful distances to which some of them extend. Not to 

 enter here into a minute discussion of all the features of this 

 widely distributed seam, it will suffice to state, that it consists 

 principally of three members, which are readily recognized. The 

 lowest is a thick bed of uncommonly pure coal, the middle a 

 layer of soft shale or fire-clay, about one foot in thickness, and 

 the uppermost or roof coal is itself a compound seam, two or 

 three feet thick, of alternating layers of coal and fire-clay. Now 

 it is a highly instructive fact, that this general triple subdivision 

 prevails throughout nearly the whole range of the seam from its 

 eastern to its western outcrops, and from the Conemaugh, in 

 Pennsylvania, into Western Virginia, for a distance of more than 

 two hundred miles, from northeast to southwest. But besides 

 this fact, each subordinate portion preserves its -own distinctive 

 features, the upper member being every where remarkable for its 

 ahernation of thin bands of coal and shale. Can any evidence be 

 more conclusive as to the uniformity of the conditions under 

 which every part of this coal-bed was produced ? There must, 

 indeed, have prevailed an almost perfect uniformity in the state of 

 the surface throughout the vast area which it occupies, as respects 

 even the formation of the thinnest of these subdivisions. Such 

 remarkable sameness of action throughout the same geologi- 

 cal horizon, appears absolutely incompatible with any mode 

 of drifting of the vegetable matter. Only one particular process 

 of accumulation promises to explain the occurrence in such cases, 

 of these thin and uniform sheets of material, of which the thick- 

 ness is often less than a foot, while their superficial area is many 

 hundred square miles. I cannot conceive any state of the sur- 

 face, but that in which the margin of the sea was occupied by 

 vast marine savannahs of some peat-creating plant, gi'owing half 

 immersed on a perfectly horizontal plain, and this fringed and 

 interspersed with forests of trees, shedding their oftal of leaves upon 

 the marsh. Such are the only circumstances, under which I can 

 imaging that these regularly parallel, thin, and widely extended 

 sheets of carbonaceous matter, could have been accumulated. 

 Independently of the above argument, based on the breadth 



