282 ANNUAL OF SCIENTIFIC DISCOVERY. 



marked, in the course of his investigations, that even these new species which 

 seem restricted to this continent, are every one of them in close relationship 

 with European forms. It deserves mention, moreover, that the commonest 

 European species are likewise the most common American ones. 



A stratigraphical analysis of the anthracite measures of Pennsylvania calls 

 for their division into two groups, a lower series, distinguished by the white or 

 very pale color of the ashes of nearly all the coal seams, and an upper series, 

 including coals as remarkable for yielding only pinkish or red ashes. Between 

 these groups there usually exists, especially in the southern or Pottsville 

 basin, a small transition group of two or three beds of gray ash, or pinkish- 

 gray ash coals. The entire number of coal seams, of a thickness admitting 

 mining, in the middle portion of the southern basin, where the whole forma- 

 tion is thickest and most replete in coal-beds, does not exceed about twenty- 

 five ; and counting those of all dimensions, the total series does not amount 

 to more than from thirty to thirty-five separate layers. 



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 can not 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 westward, seems to be 

 maintained as far as we advance in the formation ; for crossing the Missis- 

 sippi to the wide shallow coal-fields of Missouri and Iowa, the number of 

 workable 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 land-derived 

 coal-bearing portions of the carboniferous deposits. 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 surface 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 frequent alternations of coarse and fine deposits, more diversified 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 

 deposited, within the same area or extent of outcrop. The lower strata of 

 the anthracite coal measures are, indeed, remarkable for the diversity in the 

 coarseness of the sandstones, and for the unsteadiness in thickness of the coal- 

 beds themselves. Though these carbonaceous layers are the accumulations 

 of once perfectly level sea-meadows, at successive depressions of the surface, 



