Stevenson.] ^-^^ [Dee. W, 



well to refer to one given on p. 640, lying much further towai-d the west. 

 In the latter the interval between the Pittsburg and Uniontown coals is 

 said to be 245 feet, while in the former coal is only about 50 feet above the 

 Sewickly and consequently but 90 feet above the Pittsburg, 



In West Virginia the coaditions are somewhat peculiar. In the narrow 

 Panhandle at the nortti, IX and X of the Ohio section are absent. They 

 thin out before crossing the Ohio river, VIIIc. is seen on Wheeling Creek, 

 W. Va., but does not reappear on the east side of the trough. Otherwise 

 the Panhandle section offers little of interest and shows no material vari- 

 ation near Wheeling from that obtained just west from Belleair. 



In Monougahela Co., near the State line, we find on the east side of the 

 Monongahela R. the following section : Sewickly Coal, 1 ft. ; interval, 

 40 ft. ; Redstone Coal, 4 ft. ; interval, 60 ft. ; Pittsburg Coal, 6 to 8 feet. 

 On the opposite side of the river, and barely three miles away, the section 

 is Sewickly Coal, 5 ft. ; interval,. 45 ft. ; Redstone Coil, 4 ft. ; interval, 

 14 ft. ; Pittsburg Coal, lower member, 10 ft. This change results from 

 the disappearance of the heavy sandstone overlying the Pittsburg on the 

 east side of the river. 



The limestones of this group disappear somewhat abruptly soitthward, 

 and give place to shales and sandstoaes, so that satisfactory sections are 

 by no means frequent. I give for comparison the average sections for 

 Monongahela, Marion Harrison and Upshur Counties : 



1. AVaynesburg Coal. 



2. Interval Rocks... . 



3. Sewickly Ooal.... 



4. Interval Rocks.,.. 



5. Redstone Coal 



6. Interval Rocks.,. . 



183'-20?') ^' ^^'^utZlt'' 



V -6' } 240' 3" ►^y^ii^s- 



40/ -49' ) 41' 20' 



4' -5', 2' -3' 2' -4' V - 2' 



14/ -60', 70'-80'' 20'-2o' 40' -60' 



7. Pittsburg Coal I 6' -14'| 8' -9' 6' - 9 ' 3' 9"-4' 



I feel much hesitation in identifying the Redstone Coal in the last sec- 

 tioo, and think it much more likely to prove the Sewickly. The differ- 

 ence between the Marion and Harrison sections is very marked, the 

 interval between the Pittsburg and Wayoesburg being in one case 320' 

 and in the other, at most, 190'. 



Conclusions. — After a careful study of the barren and upper coal groups 

 throughout the northern portion of the great bituminous trough, I am 

 convinced that as a whole the subsidence was regular, approaching uni- 

 formity, but that locally there were bulgings or other irreguliarities, such 

 as could not fail to accompany any operations so extensive. The lack of 

 parallelism results from the conditions of deposition, which rendered par- 

 allelism impossible. The two groups referred to were deposited in a great 

 trough whose eastern boundary was the Alleghany Mountains ; the west- 

 ern, the Cincinnati axis.* They diminish quite regularly in thickness, east 

 and west, from a centi-al area between the Ohio and the Monongabela 



* The substance of this portion of the paper was published March 4, 1873, in Annals 

 Lye. Nat. Hist., Vol. X. pp. 247, et scq. 



