BITUMINOUS AND aNTHRACITIC. 447 



the known length of the tract actually occupied by it, as exceed- 

 ing the above-mentioned two hundred and twenty-five miles, 

 throughout which it is uninterruptedly traceable. If we now 

 take into account the fifty additional miles of breadth which the 

 bed once possessed, its former area must have been at least thirty- 

 four thousand square miles, a superficial extent greater than that 

 of Scotland or Ireland. 



Though the above is, perhaps, the greatest extent of surface, 

 which it is in our power positively to assign to this bed of coal, 

 the proofs of a prodigious denudation of the strata, throughout the 

 districts bordering its present outcrop, are so irresistible, that I 

 consider the dimensions here given as bearing actually but a 

 small proportion to the real ancient limits of the stratum. I con- 

 sider it, indeed, probable, that this seam is identical with the great 

 bed which occurs in all the anthracite basins, and w^hich displays 

 a similar degree of constancy in its features. Opportunities for 

 research have not yet occurred to enable me, however, to produce 

 evidence as to this point, of a sufficiently conclusive character. 

 Should such an identity be estabfished, we shall then behold, in 

 all its conditions of gradation from anthracite to semi-bitumi- 

 nous and highly bituminous coal, a single stratum, measuring, at 

 the most moderate calculation, four hundred and fifty miles in 

 length, and two hundred miles in breadth, and covering a space 

 of at least ninety thousand square miles. But, restricting our 

 attention for the present to those limits, which it did undoubtedly 

 once occupy, it is still by far the most extensive coal-bed yet ex- 

 plored in any country, and th® mere fact of its great extent must 

 exert an influence on our views concerning the conditions under 

 which the whole coal-formation originated. 



The general uniformity in the thickness of this superb bed, 

 throughout so vast a region, and at the same time the regular 

 and gentle gradation which it experiences in size, when we trace 

 it from one outcrop to the other, are features not less remarkable 

 than its enormous length and breadth. In the most southeastern 

 basins, w^here it is most developed, its total thickness is from twelve 

 to fourteen feet ; while in the basins between the Chestnut ridge 

 and the Monongahela river, it usually measures from ten to 



