THE IRON ORES. ways, Bi A 
follow, and sometimes they are so sparsely distributed that though the 
aggregate amount of ore in a bed of shale or clay is considerable, it 
will not pay for working. 
In quality, these ores hold a good rank. They are often very 
kind and easy to smelt. The weathered kidneys are almost always so. 
The unweathered masses are frequently too close and stubborn for use 
in charcoal furnaces. They contain from 35 to 50 per cent. of metal- 
lic iron. 
There are 5 or 6 pretty well marked horizons of kidney ore, some 
of which are quite persistent and widespread. 
The block ores are so called from the fact that they are found in 
horizontal and almost continuous sheets of uniform thickness, but these 
sheets are of chemical not mechanical origin. They range in thickness 
from one or two inches to one or two feet, but the ores that are worked 
are mostly between 4 and 8 inches in thickness. The separate blocks 
have the same general structure as the kidney ores last described. 
They show their concretionary origin in the concentric layers that 
weathering reveals. These blocks are often fitted to each other like 
the separate blocks of a tesselated pavement. 
They bear a peculiar relation to the coal measure limestones. 
Without exception, the leading block ores. of the field are borne by 
these limestones, or else, the ores seem to replace and substitute them. 
They deserve to be called limestone ores from this point of view, and 
they are so called in some localities, but in Ohio, this name is mainly 
reserved for other phases of iron accumulation. 
The block ores of our scale are often mellow and excellent. The 
weathered ores average a little more than 40 per cent. of metallic iron 
as a rule. 
There are three chief horizons of these ores, and two of them are 
remarkably persistent, stretching with the limestones that bear them 
entirely around the field. 
The ores that are known as limestone ores present two distinct 
phases. The name is mainly confined to the Hanging Rock district of 
Southern Ohio, where it is applied to one well-known and very valuable 
seam, viz., the ore b:2=2 wy the Ferriferous limestone of the general 
scale. The designation “limestone ore” is specific in this portion of 
the State, being exclusively applied to this seam. The ore overlies the 
limestone, sometimes graduating insensibly into it, and sometimes 
