THE IRON ORES. 423 
below the Lower Mercer limestone. The range of intervals is small, 
not exceeding 10 feet. 
The only ore of the counties to the northward with which it can 
be correlated is the Junction City or Union Furnace block ore, and 
this possibly takes the place of the Lower Mercer coal. It is not 
claimed that this correlation is established on any stratigraphical con- 
nections between the fields, but the regular expansion of intervals to 
the southward would throw the Junction City ore about to the level of 
the Boggs ore in Scioto county. | 
Block Ores. 
The three ores that are next reached in ascending order are by far 
the most important of the division, and are among the well-marked and 
well-known ores of the field. Two of them, moreover, are of the 
persistent class, coming into the present sections from every district 
which our review has thus far traversed. They are the block ores of 
the Mercer series. There are but two ores in the rest of the field, 
accompanying this group, but a third and intermediate one is added in 
the Hanging Rock district. The lowermost certainly covers the Lower 
Mercer or Blue limestone, the most wonderfully persistent little stratum 
of the entire geological scale of Ohio. It has more hundreds of miles 
of outcrop than it has feet in thickness. The uppermost of the three 
ores also frequently covers a limestone or flint, which matches in all 
respects to the Upper Mercer horizon, to which the flint and ore are 
referred. There remains an ore of frequent occurrence and quite wide 
distribution between these two ores. It is commonly known as the 
sandblock ore. It is generally nearer to the upper block than it is to 
the lower, being 12 to 20 feet from one and 25 to 35 feet from the other. 
The lower block ore is known by several local designations. It is 
called the blue limestone block, in Jackson county, the little block and 
the fine block at other points. It is thin in southern Ohio, seldom ex- 
ceeding 6 inches in thickness, and ranging where worked from 4 to 6 
inches, but it is persistent, and its quality is steady and excellent. It: 
is nowhere mined in drifts, but the benchings for it skirt a great many 
hills and a great number of miles of outcrop. All of the western fur- 
naces, except Jefferson, use it, but none of them make it a reliance. 
The middle ore or sandblock is on the whole a better ore than its 
name implies. Its use is not generally encouraged at the furnaces, but 
