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 thiekening aad 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 
erns. 
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 
