J 



412 H. D. Rogers's Observations on 



frequent alternations of coarse and fine deposits, more diver- 

 sified and rapid changes in the thickness, composition, and 

 arrangement of the strata, both of the mechanical deposits and 

 the life-derived beds of coal, and the far greater mutability 

 and inconstancy of all those strata, even the most quietly de- 

 posited, within the same area or extent of outcrop. The 

 lower strata of the anthracite coal-measures are, indeed, re- 

 markable for the diversity in the coarseness of the sandstone, 

 and for the unsteadiness in thickness of the coal-beds them- 

 selves. Though these carbonaceous layers are the accumula- 

 tions of once perfectly level sea-meadows, at successive de- 

 pressions of the surface, it is evident, from their comparatively 

 rapid thickening and thinning, and frequent coalescing and 

 diverging, that the floors upon which they were collected were 

 neither so wide as those which open the vegetation that result- 

 ed in the bituminous coal-beds, nor so uniform and gradual 

 and horizontal in their slow movements of elevation and 

 depression. 



Commensurate with the more fluctuating size, and more re- 

 stricted range of these lower coal-seams, is a greater incon- 

 stancy and diversity in their fossil flora. The more widely 

 extended upper beds appear to exhibit a more limited specific 

 vegetation, expanded over wider areas. 



As far as our researches have gone, we notice that the lower 

 strata, both in the anthracite measures, and in the great Appa- 

 lachian coal-field, abound in the larger species, especially in 

 Lepidodendra, while the higher seams are characterized by 

 the smaller herbaceous species, most generally the herbaceous 

 ferns. 



We conceive that the large proportion of species common 

 to the coal strata of North America and Europe clearly esta- 

 blishes identity of age between the two deposits, and a close 

 accordance, if not identity, -in the geographical and climatal 

 conditions prevailing at their formation. A yet closer agree- 

 ment is noticeable between the species found in the several 

 coal-fields of the United States. Indeed, so alike are all the 



