434 ORIGIN OF THE APPALACHIAN COAL STRATA, 



rocks of the Allegheny mountains, by Mr. Conrad.* Other me- 

 moirs have appeared upon local portions of the coal region of. 

 Pennsylvania, but I am not aware that their details h^ve con- 

 tributed to any of the general laws and results here presented. 



Of the Limits of the Appalachian Coal Strata. 



The extensive Appalachian coal formation, embraces all the 

 detached basins, both anthracitic and semi-bituminous, of the 

 mountain chain of Pennsylvania, Maryland, and Virginia, and 

 also the vast bituminous trovigh, lying to the northwest in Penn- 

 sylvania, Ohio, Virginia, Kentucky, Tennessee, and Alabama. 

 I shall endeavor presently to show, that all these coal-fields, ex- 

 tending from the northeastern counties 9f Pennsylvania, to the 

 northern part of Alabama, and from the great Appalachian val- 

 ley, westward into the interior of Ohio and Kentucky, include 

 only a portion of the original formation, immense tracts having 

 been destroyed by denudation. A comparison of the coal strata 

 of contiguous basins, has convinced me, that they are only de- 

 tached parts of a once continuous deposit ; and the physical struc- 

 ture of the whole region most satisfactorily confirms this idea, by 

 showing that they all repose conformably on the same rocks ; the 

 more or less insulated troughs in which they occur, merely being 

 separated by anticlinal tracts of greater or less breadth, from which 

 denuding action has removed the other portions of the formation. 

 This distribution of the coal in a series of parallel and closely 

 connected synclinal depressions, is a dh-ect result of the system 

 of vast flexures, into which the whole of the Appalachian rocks 

 have been bent, by the undulatory movements that accompanied 

 the final elevation of the strata, and terminated the era of the 

 coal. 



Many of the general phenomena about to be described, seem 

 to belong, in an equal degree, to the wide coal basins of equiv- 

 alent age, which lie remote from the Appalachian chain, far to 

 the northwest, namely, that of the State of Michigan, and that 

 which occupies a part of Indiana, Illinois, and Missouri. I shall 



♦See Trans. Geo. Soc. of Pennsylvania, 1S35. 



