144 GEOLOGY OF OHIO. 
In some of our coals, especially in the Massillon field, the joints, 
though well defined, are close and do not readily release the coal, and 
consequently a larger proportion of powder is used here to free the coal 
than in any other Ohio field. The miner often calls eee planes of 
division the “slips” of the coal. 
When for any reason the regularity of these joints is interfered 
with, the ‘‘grain” of the coal is said to be “short,” or “ crooked,” or 
“curly,” and generally the labor of mining is increased, sometimes to a 
notable extent, by such irregularity. 
When the main joints are well developed, and the secondary joints 
less perfectly, we have a “long-grained” coal. This term is also used 
for slaty or inferior coal in some parts of the field. The Upper Free- 
port seam gives a good illustration of the former case throughout 
Eastern Ohio. Its faces are bright and clean, and the coal splits 
naturally along them in blocks from 6 to 18 inches thick, but the end 
joints, though present, do not so thoroughly divide the coal, and the 
consequence is that we have the approximately monolithic structure 
that characterizes the leading fields of this coal, viz., Salineville, Dell 
Roy and Cambridge. The coal tends to mine in oblong rather than in 
cubical blocks. 
More detailed statements will be made upon these topics in connec- 
tion with the description of the different seams, and especially in the 
chapter upon the mining of coal. These condensed and general state- 
ments are necessary to make the accounts of the several! fields readily 
intelligible. 
CLASSIFICATION OF OHIO COALS. 
All the coals of the Ohio series belong to the bituminous division, 
but they are further divisible into three well-marked groups, viz.: (1) 
Open burning coals; (2) Cementing coals ; (3) Cannel coals; the first 
two of which are sometimes termed cubical coals. 
Newberry describes these divisions as follows (vol. II, pp. 
122-3-4) : 
“The first variety enumerated includes those that do not coke and 
adhere in the furnace, and such as can be used in the raw state for the 
manufacture of iron. They have generally a distinctly laminated struc- 
ture, and are composed of bituminous layers, separated by thin parti- 
tions of cannel or mineral charcoal, materials which do not coke. 
