THE CARBONIFEROUS SYSTEM. 123 



here 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. Hence 

 the bitumen in them — relatively small in quantity — is held in cells, and 

 cannot flow together so as to give the mass a pasty, coherent character. 

 In Ohio the lowest stratum of this series (Coal No. 1, the Briar Hill, 

 Massillon and Jackson coal) is generally a furnace coal. As it occurs in 

 the Mahoning valley, it is a type and standard of the class to which it 

 belongs, and is one of the best furnace fuels known, half the iron pro- 

 duced in the State being made with it. In consequence of the structure 

 of our coal basin (Coal No. 1 underlying all the others, and dipping to- 

 ward the south and east), it is for the most part covered by the underly- 

 ing rocks, and whether it extends beneath the center of the basin is yet 

 uncertain. Coal No. 6 — the " Great vein" the Straitsville, the Steubenville 

 shaft seam, etc. — has locally this open burning character. 



The second class, or cementing coals, are such as have few partitions, 

 but show upon fracture broad surfaces of pitch-like bitumen. These, to 

 a greater or less degree, melt or agglutinate by heat, forming what black- 

 smiths term a hollow fire. This property causes them to choke up the 

 furnace and arrest the equal diffusion of the blast through the charge ; 

 hence they cannot be used in the raw state for the manufacture of iron, 

 but must be coked. This process of coking consists in burning off 

 the bituminous or gaseous portion, which leaves the coal in the condi- 

 tion of anthracite, except that as this change is effected without pres- 

 sure the resulting material is cellular and spongy. Coals of this charac- 

 ter, when free from sulphur — their great contaminating impurity — are 

 used for the manufacture of gas ; the volatile portion driven off in the 

 retorts serving the purpose of illumination,-while that which remains is 

 coke, and may be used as fuel. By far the greater portion of our coals 

 are of the coking variety. Up to the present time they have been but 

 sparingly used as furnace fuels, from the fact that they generally contain 

 an objectionable amount of sulphur. Many of them are capable, how- 

 ever, by proper treatment, of yielding an excellent coke, and the future 

 industries of the State largely depend upon the degree of intelligence 

 and energy shown in the utilization of our cementing coals. 



The cannel coals are more compact and homogeneous in texture, and 

 contain a larger percentage of volatile matter than the others ; also, the 

 gas they furnish has higher illuminating power ; hence they would be 

 used to the exclusion of all others for the manufacture of gas, but that 

 the coke yielded by them is of inferior quality. They are, therefore, 



