172 GEOLOGY OF OHIO. 
and Bellaire the space between Coals No. 8 and No. 10 increases by more 
than 100 feet; establishing a fact which is fatal to the theory of the par- 
allelism of coal seams. 
Between Bellaire and Wheeling the cliff which borders the valley has 
been so much quarried away that its structure is visible almost at one 
view. The Pittsburgh coal is here very near the grade of the railroad, 
and three coal seams are seen above it. A want of parallelism is visible 
among all of them, but the most conspicuous deviation is seen in the 
first two seams above the Pittsburgh. The interval which separates 
these varies locally from twelve to thirty-five feet. Cases similar to 
those I have cited may be found in every county within the coal basin, 
but enough have been given to show that our coal seams are never abso- 
lutely parallel over any considerable area. That they are sometimes 
approximately parallel for long distances is true; and this fact serves as 
an important general guide in tracing them. For passing from one 
series of outcrops to another, not too far away, when one well-marked 
member of the series is found we know about where to look for the others ; 
but to hold rigidly to the theory of parallelism, and to deny the continu- 
ity of all coal seams which do not exhibit uniformity in the distance that 
separates them, would be to throw our whole system of coals into con- 
fusion, and render every effort for their classification abortive. 
Although this subject has, perhaps, already occupied more space than 
it deserves, I venture to call the attention of those who are interested in 
it to the results of the wide experience in coal geology which has been 
gained in other states and countries than ours. These will be found in 
the valuable papers of Prof. Dawson, contained in his “Acadian Geology,” 
the reports of Profs. Worthen and Cox on the geology of Illinois and 
Indiana, and those of Profs. Rogers and Lesley on the geology of Pennsyl- 
vania. Iwould also specially cite the Report of the British Coal Commis- 
sion, Vol. I., pp. 121 and 141, and the Memoirs of the Geological Survey 
of the United Kingdom, Geology of Wigan, by Edward Hall, p. 17. 
The economical bearings of this question will also be referred to in the 
volume of this Report devoted to Hconomic Geology. 
“TROUBLES” IN COAL SEAMS. 
Faults in which the displacement amounts to more than one foot are 
very rare in the Ohio coal field. Smaller ones are not at all uncommon, 
and almost every coal mine of any considerable extent will show one or 
more. These are in all respects except dimensions exact copies of the 
ereat faults by which the coal strata of Kneland are so much broken up. 
The coal is frequently found cut by them more smoothly than it could 
