284 HE. B. Andrews—Comparison between the Ohio and 
ides to take the horizon of the Pittsburgh seam of coal as the 
ase of measurement. 
This seam is of wide extent, being 225 miles long and about 
100 miles wide, and is easily recognized by geologists. It has 
been asserted that this seam was formed in a trough with the 
Alleghany mountains forming a sloping side on the one hand 
and the Cincinnati uplift on the other, and as the subsidence— 
which is conceded to have been regularand uniform—continued, 
the marsh, with its accumulated vegetable matter, crept up 
either slope. In time the center or lowest part was buried by 
sediments and new land surfaces were formed on which vegeta- 
tion grew and other resulting seams of coal stretched across the 
trough from side to side like the chords of an are, but all 
coalescing with the great seam ever rising along the margins to 
meet them. I know of no proof whatever that the price 
mountains were uplifted just before the era of the upper coal- 
measures, nor is there any that the slope on the side of the 
Cincinnati uplift differed at the time the Pittsburgh seam was 
formed from what it had been during the era of the lower coal- 
measures. ‘There is, furthermore, no proof that the upper and 
‘This seam occupies nearly the center of the northern and 
wider part of the Alleghany coal-field and extends through 
portions of Pennsylvania, Ohio, and West Virginia. It 
Now, if we take this seam of coal and follow around its line 
of outcrop and measure from it down to the base of the pro 
ductive coal-measures, we find the intervals quite uniform 
through the larger part of the circuit. In Ohio, according t0 
rt. Newberry’s measurements and my own, it is from 700 > 
800 feet. In Pennsylvania on the Alleghany river north © 
Pittsburgh it is reported by Prof, H. D. Rogers to be from 600 
to 700 feet ; or 800 feet including the conglomerate underneath. 
In the northern part of West Virginia, a little south of the 
Pennsylvania line, it is reported to be 500 feet. But in West 
