444 ORIGIN OF THE APPALACHIAN COAL STRATA, 



be sufficient here to refer to what I have above stated, respecting 

 the oceanic and shore rocks, and to appeal to the ai'gument that 

 the coarser or more irregularly strewn the materials of a sti-atum 

 are, the more violent must have been the current which trans- 

 ported them. "With these considerations before us, we cannot 

 fail to perceive, in the Appalachian coal-strata, the monuments of 

 many alternate periods of movement and total or comparative rest. 

 If it be conceded, that each of the purer beds of limestone, re- 

 markable for the extreme fineness of their texture, and the absence 

 of foreign sedimentary matter, is the index of a longer or a shorter 

 interval of tranquillity in the waters, we shall discern (omitting 

 for the present all similar inferences to be derived from the coal- 

 seams) a much gi-eater number of such separate periods, than a 

 mere enumeration of the individual beds would indicate, unless we 

 attend to the interstratified shales and marls. These last-men- 

 tioned strata, generally assuming, as we go eastward, a thicker 

 and coarser type, furnish as unequivocal a record of disturbances, 

 as if the'spaces they occupy between the beds of limestone, were 

 fiUed by the coarsest mechanical aggi'egates. 



One of the most interesting general questions connected ^^^th 

 the land and sea-produced strata, relates to the physical geography 

 of the ancient coast, near to which they were deposited, and the 

 inquiry at once suggests itself, whether the receptacle of these 

 various sediments was an extensive estuary, receiving the silts of 

 some gigantic river or rivers, or a vast expanse of shallow sea, 

 bounded by a long line of coast, upon which the successive de- 

 posits were formed by a very different agency from any we can 

 ascribe to ordinary fluviatile or littoral currents. 



Of the Phenomena connected with the Coal-Seams. 



Great extent of certain individual coal-beds. Passing, in the 

 next place, to an examination of the most interesting portion of 

 the coal strata, the coal-seams themselves, we discover in the facts 

 connected with their range and distribution, in the structure of the 

 coal, and in the nature of the beds in immediate contact with the 

 seams, several general laws, tending to afford us a still better in- 



