‘ the Coal-fields of Pennsylvania. 413 
anthracite basins in their fossils, that Mr. Lesquereux already 
recognizes more than twenty familiar European species as 
common to these once continuously united coal-fields. It has 
been indicated above, that the two different groups of the coal 
strata of Pennsylvania, the lower or white ash, and the upper 
or red ash, are characterized by somewhat different species, 
though these more or less intermingle. Satisfied of this fact, 
of a general prevalence of certain forms in certain parts of the 
coal-measures, we have aimed at carrying our inquiry a step 
farther, to ascertain whether or not any or all of the individual 
coal-seams themselves are separately recognizable by their fossil 
Plants. Undoubtedly, in some of the broadly deposited and 
uniformly conditioned coal-beds and coal-slates of the western 
bituminous coal-fields, we do observe a most striking preva- 
lence of the same species within the same layer, on compara- 
tively wide areas ; but amid the more irregularly accumu- 
lated beds, of especially the lower or white ash anthra- 
cite strata, formed on a less stable portion of the nowhere 
absolutely stationary crust, the inconstancy in the vegetation 
of even the same coal-seam is, for the most part, if not even 
quite, too great to permit us to attempt to identify it by its 
fossils merely, Again, in some instances, coal-beds which are 
demonstrably different, are almost absolutely identical in their 
Ossils. This is the case with the “Gate” and “Salem” 
Coals, near Pottsville. So strikingly alike are they in their 
Vegetation, that Mr. Lesquereux strongly inclines to regard 
them as but the detached parts of originally one sheet of coal, 
and to suspect that there is some error of obscurity in my sec- 
tion, which shows them to be separated by several hundred 
feet of strata, including a number of beds of coal. Of the 
validity of the proofs, showing the so-called Salem vein, to be 
different coal from the Gate vein, and several stages higher in 
the series, there cannot, however, be any question, and the 
Paleeontological evidence for identity must give way before the 
igher and decisive demonstration from superposition, of their 
difference in age. 
