438 ORIGIN OF THE APPALACHIAN COAL STRATA, 



shall not here attempt a minute description of all the carbonifer- 

 ous rocks ; and, to confine these remarks within as small a com- 

 pass as possible, I shall restrict them to the main or upper coal 

 measures, since these are the beds which best display the physical 

 conditions under which the strata were accumulated. 



Nature of the Coal Strata. 

 Assuming it as susceptible of demonsU-ation, that all the various 

 coal basins, bituminous and anthracitic, of Pennsylvania, Ohio, 

 Maryland, Virginia, Kentucky, and Tennessee, were, as above 

 stated, originally united, we may consider the whole as one great 

 formation, in which some highly interesting gradations in the 

 type and composition of the beds may be traced. To call atten- 

 tion to these phenomena of variation is indeed the main object of 

 this paper, since by them only can we arrive at a true theory of 

 the conditions under which the whole were formed. A compre- 

 hensive classification of the strata, shoM^s the following principal 

 varieties. 



1. Rocks of mechanical origin, of every gi'ade of coarseness, 

 from the smoothest fire-clay, to exceedingly rough siliceous con- 

 glomerates, the whole including within these extremes a wide 

 variety of shales, marls, argillaceous sandstones, and quartzose 

 grits. 



2. Limestones, both pure and magnesian, in strata of all thick- 

 nesses, from thin bands and narrow layers of detached nodules, to 

 beds measuring from fifty to one hundred feet in depth. Some 

 of the limestones contain a considerable amount of argillaceous 

 and siliceous matter, and many of the thicker deposits consist of 

 alternating layers of limestone and soft shale. Though a few of 

 these calcareous strata are remarkably destitute of fossils, they are 

 rarely found to be altogether deficient in organic remains, when 

 widely and diligently searched ; and some of them quite iibound 

 in them. It is especially deserving of note, that the genera are 

 such as invariably indicate oceanic habits. This fact is of the 

 more importance, since some of the limestones occur in imme- 

 diate contact with beds of coal, and with shales and other strata 

 containing the remains of terrestrial vegetation. 



