THE IRON ORES. 375 
shale to secure an average of an inch of ore. The quality is of the 
best. The ore will yield 60 per cent. and upwards of metallic iron, 
but in practically the whole field that these nodules occupy, the quantity 
is too small to justify working under the present conditions of iron 
manufacture. This ore, in other words, has no present value, and it 
does not seem probable that it can ever be profitable to mine it. Each 
new observer that comes into the field, however, will be impressed with 
its intrinsic excellence, and will need to satisfy himself by independent 
observations that it does not exist in such a condition as to warrant 
mining before he will be willing to abandon so promising an addition 
to the iron making materials of Ohio. 
There is not a single seam of ore above the Mahoning sandstone 
that is regularly mined in Ohio at the present time. 
CLASSIFICATION OF THE ORES OF THE LOWER CoAL MEASURES. 
As has already been stated, all of the native iron ores of the State 
which are turned to present account for furnace use are derived from 
the Lower Coal Measures. One or two trifling exceptions have been 
already noted in the cases of the block ore borne by the Sub-carbonif- 
erous or Maxville limestone and the rough ore that caps the conglom- 
erate, but the statement scarcely requires qualification for such excep- 
tions as these. | 3 | 
The ores of the Lower Coal Measures were all accumulated under 
the same general conditions, 1. e., as carbonates of iron in the marshes 
and swamps of.the period to which they are referred, but they have 
assumed several distinct forms which afford a convenient basis of 
classification. 
They can be divided into the following groups: 
I. The stratified or mechanically-formed ores. 
II. The concretionary or chemically-formed ores. 
The first group includes all those ores that bear the marks of 
having been accumulated in water, or at least in successively formed, 
horizontal sheets, after the fashion of ordinary sediments. The car- 
bonate of iron that they contain has of course had a chemical his- 
tory similar to that of the same mineral in other ores, but the arrange- 
ment of the carboniferous or shaly matters with which the iron is 
associated is due to stratification. ‘These ores are variously known as 
