the Coal-fields of Pennsylvania. 411 
In the bituminous coal-measures west of the Alleghany 
Mountains, the whole number of workable seams is less than 
one half of that above named, as belonging to the anthracite 
formation, while, including the thinner and less persistent 
beds, the entire series cannot there amount to more than 
eighteen or twenty. That portion of this great Appalachian 
coal-field, which lies within Ohio, appears to possess even 
somewhat fewer than the eastern half in Pennsylvania, the 
beds suitable for mining being estimated at seven, and the 
small seams about ten, in addition. 
Advancing westward to the great coal basin of Indiana and 
Illinois, the coals thick enough for working are counted at 
only six, and the thin ones proportionately few ; and this re- 
markable progressive reduction in the coal-beds, going west- 
ward, seems to be maintained as far as we advance in the 
formation ; for crossing the Mississippi to the wide shallow 
coal-measures of Missouri and Iowa, the number of the work- 
able beds there believed to exist, does not amount to more 
than three or four. Accompanying this interesting gradation 
in the amount of coal, there occurs an equally noteworthy 
diminution in the thickness and coarseness of the associated 
strata, showing a progressive thinning down of the whole of 
the land-derived coal-bearing portions of the carboniferous 
deposits. -A future comparison of the fossil plants of these 
broad successive coal basins will probably disclose a corres- 
ponding reduction in the number and variety of the species, 
a view already suggested by their relative paucity in the bitu- 
minous coal-fields of western Pennsylvania and Ohio, as mea- 
sured by their abundance in the anthracitic basins. 
Wherever I have studied either of the anthracite fields, of the 
great Appalachian basin, I have remarked that the lower or 
“white ash” division of the coal-measures, gives indications 
of more violent and frequent disturbances of level in the sur- 
face, at the time of the deposition of the strata, than are 
noticeable in the composition of the upper or “red ash" part 
of the formation. Among the -proofs are, more abrupt and 
