COAL. 91 
Thickness, in inches, of Pittsburg coal in the Amity quadrangle. 
Mine. 
Thickness. 
Average. 
Greatest. 
Least. 
62 
64 
60 
78 
60 
■57 
72 
54 
66 
64 
64 
64 
64 
72 
71 
73 
73 
Rich Hill 
74 
74 
76 
76 
70 
Ellsworth No. 2 
68 
Ellsworth No. 3 
70 
70 
In the course of the field work several detailed sections were meas- 
ured in various parts of the area. These measurements are given 
graphically in PI. V. Except in a few places the bed is double, sepa- 
rated by a fire-clay parting of varying thickness. Here and there 
a third division is present, and in many places the bed is interrupted 
by other clay partings, but generally these are not persistent. 
The roof division or portion above the clay parting is variable. 
In thickness it runs from 1 inch up to 4 feet. In some places it con- 
sists of a single bench, but more commonly is broken up into two or 
more benches, separated by shale or clay. The coal of this division 
is usually poor, containing a large proportion of ash. 
The main clay separating the roof and lower divisions varies from 
a fraction of an inch up to 15 inches in thickness. The lower divi- 
sion of the Pittsburg coal varies in thickness from 3 J feet to 5 feet 
10 inches and is the portion of the coal mined throughout this sec- 
tion of the field. The most characteristic feature of this division 
consists of two very persistent partings, which, as a rule, occur 2 to 3 
feet from the bottom. They are known as the "bearing-in bands," 
and with the coal between them make up the "bearing-in coal." In 
few places are they over half an inch thick ; commonly they are con- 
siderably thinner. The interval between them varies from 1 inch to 
2^ inches. The name " bearing-in" has been applied because this 
bench is chosen by the miner as the easiest layer on which to work to 
undercut the overlying coal. The bearing-in coal is thrown out in 
mining. The bench is represented in all but two of the sections in PI. V, 
and is probably present in the others, but was overlooked in taking 
measurements. In one country bank (section 5) the place of this 
bench is taken by fire clay. The bearing-in coal separates the lower 
division of the Pittsburg coal into two portions, the upper of which is 
known as the breast coal and the lower as the brick coal and bottom 
