THE CARBONIFEROUS SYSTEM. 163 
dimensions is very unreliable. Its characteristic features are well shown 
in the cut west of Barnesville, where my attention was called to it by 
Prof. Stevenson. At one end of the excavation it is barely six inches in 
thickness, while at the other it shows a total of five feet four inches, con- 
sisting of coal, one foot; shale, four inches; coal, four inches; shale, four 
inches; coal, four inches; shale, two feet; coal, one foot. Seven miles 
east from Barnesville, where it is exposed in a railroad cut, it is about 
one foot thick, and parted in the middle by a thin layer of limestone. 
Near St. Clairsville, in the same county, it is rudely worked, and shows 
three feet of very impure coal, resting almost immediately upon a foot 
of limestone. Near Bridgeport, opposite Wheeling, it is three feet six 
inches thick, roofed by six inches of impure blackband, which is over- 
lain by two feet of alternating bands of bituminous and ordinary shale. 
On a run four miles west from Bellaire, and just south of the railroad, it 
suddenly thickens out and becomes a confused mass of coal and shale, . 
not less than fifteen feet thick, and totally worthless. 
In Harrison and Jefferson counties it is never more than two feet 
thick, and is seen only near the tops of the highest hills, and has no 
economical value. (Stevenson. ) 
Coal No. 12 is generally found in the highlands which border the Ohio 
opposite Wheeling. It is usually from a few inches to two feet in thick- 
ness, but is locally, near the Ohio, developed into a dry coal six feet in 
thickness, but heavily charged with pyrites. 
Coal No. 18 lies some seventy feet above the last, is very thin, and has 
no practical value. It is limited to the summits of the divide east of 
the Ohio, on and south of the Baltimore and Ohio Railroad. 
DISTRIBUTION OF THE LIMESTONES OF THE UPPER COAL MEASURES. 
If it is true, as has been supposed, that Coal No. 10 of the Belmont 
section is the Cumberland coal of the south-eastern counties of the State, 
it will be seen to thicken toward the west, and, its basin may be said to 
lie west of the Ohio. This is also indicated by the limestones with 
which this coal is associated, and which are thinner and less numerous 
in the Upper Coal Measures of West Virginia and Pennsylvania, after 
passing above the “Great limestone,” which there lies over the Pittsburgh 
seam. We are in these facts furnished with evidence of another change of 
the center of gravity, if we may use the term, in the progressive .sub- 
sidence of the Alleghany coal field. Following back the history we have 
traced, and measuring the spread of marine conditions by the reach, and 
their continuance by the thickness of the limestones, and tracing the 
local depressions of the different epochs by the thickening of the de- 
