GEOLOGY. 283 



it is evident, from their comparatively rapid thickening and thinning, and fre- 

 quent coalescing and diverging, that the floors upon which they were collected 

 were neither so wide as those which grew the vegetation that resulted in the 

 bituminous coal-beds, nor so uniform and gradual and horizontal in their slow 

 movements of elevation and depression. Commensurate with the more fluc- 

 tuating size and more restricted range of these lower coal seams, is a greater 

 inconstancy 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 hi the great Appalachian coal field, abound in the 

 larger species, especially in Lepidodendra, while the higher seams are charac- 

 terized by the smaller herbaceous species, most generally the herbaceous ferns. 

 "We conceive that the large proportion of species common to the coal strata 

 of Xorth America and Europe clearly establishes identity of age between the 

 two deposits, and a close accordance, if not identity, in the geographical and 

 clirnatal conditions prevailing at their formation. A yet closer agreement is 

 noticeable between the species found hi the several coal fields hi the United 

 States. Indeed so alike are all the anthracite basins in their fossils that Mr. 

 Lesquereux already recognizes more than 20 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 further to ascertain whether or 

 not any or all of the individual coal seams themselves are separately recogniz- 

 able 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 prevalence of the same species 

 within the same layer, over comparatively wide areas ; but amid the more 

 irregularly accumulated beds, of especially the lower or white ash anthracite 

 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 demon- 

 strably different, are almost absolutely identical in their fossils. This is the 

 case with the "Gate" and the "Salem" coals, near Pottsville. So strikingly 

 alike are they hi 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 section, 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 vein to be differ- 

 ent coal from the Gate vein, and several stages higher in the series, there can 

 not, however, be any question, and the palaeontological evidence for identity 

 must give way before the higher and decisive demonstration from superposi- 

 tion of their difference hi age. 



