THE CARBONIFEROUS SYSTEM. 141 
Greentown it is four to five feet thick, a bituminous coal of good quality. 
At Alliance, on the eastern border of Stark county, Coal No. 4 is reached 
and worked in the Alliance Fire-Clay Company’s shaft. This is also the 
coal which is mined at Atwater, and penetrated in the shaft sunk at 
Edinburgh. In the former locality it is from four to five feet in thick- 
ness, with a parting in the middle. It is here an open-burning, semi- 
cannel coal, much like what it is at Uhrichsville, and in the shaft of 
the Trumbull Company on the Sandy, below Waynesburg. Its lime- 
stone is here wanting. 
In the valley of Yellow Creek Coal No. 4 is represented, as J have sup- 
posed, by the Hammondsville “Strip vein,” here as at Atwater without 
its limestone. 
On the eastern border of the State Coal No. 4 is probably represented 
by the remarkably pure bituminous coal of Letonia and the cannel of 
Canfield and Darlington, and hence is identical with the Kittanning 
coal of Pennsylvania. The limestone over Coal No. 4 is that called by 
Prof. Andrews the Putnam Hill limestone. It is also frequently referred 
to in our reports as the gray limestone, to distinguish it from that over 
Coal No. 8, which is designated as the blue limestone. The difference in 
color indicated by their names prevails over several counties, but is not 
universal. As has been before stated, both limestones are highly ferrif- 
erous. The iron ore which accompanies them is sometimes in the form 
of tiers of nodules of “ kidney ore,” which le just above them ; some- 
times as “plate ore,” or sheets of calcareous clay, or on stone resting on 
them ; or, finally, ‘block ore,” 
pletely replacing the limestones. 
It often happens, also, that these limestones become earthy or bitu- 
minous, and are converted into blue or black calcareous shale, full of the 
fossil shells which abound in the limestones when purer. 
The Putnam Hill limestone locally assumes still another phase which 
IT have not observed in the lower or Zoar limestone, 7. e., it is converted 
into a hydraulic lime by the addition of a considerable percentage of 
earthy matter. In such circumstances it becomes somewhat laminated, 
but retains its hardness, and frequently becomes almost as sonorous as 
phonolite. Its thickness is usually increased. When freshly broken it 
is still blue, but when weathered, its lime superficially dissolved out, and 
its iron oxidized, it becomes brown, or even yellow, and would hardly be 
recognized as a limestone. When assuming this phase it is sometimes 
highly fossiliferous, and has then supplied us with by far the largest 
portion of the Coal Measure mollusks obtained in the prosecution of the 
survey. At Flint Ridge, at New Philadelphia, where the road to the 
a stratified mass of ore more or less com- 
