LIMESTONE. 119 
has naturally formed a very good soil, and, as a rule, no burned lime 
is necessary on the land. In a few instances only were evidences 
that lime had been burned seen in the fields. 
The principal limestone beds in the area are described from the 
bottom upward. 
LIMESTONES BETWEEN THE PITTSBURG AND WAYNESBURG COALS 
(MONONGAHELA formation) . 
FISHPOT LIMESTONE. 
The Fishpot limestone underlies the Sewickley coal at a distance 
of a few feet. It was originally named by Stevenson from Fishpot 
Run, in the southeast corner of Washington County, but I. 0. White 
has applied the term Sewickley to this same limestone. During the 
present survey this bed was observed underneath the coal on Fish- 
pot Run, where 30 feet of it is reported, and on Mingo Creek. En 
sinking the Enterprise mine shaft, 1 mile north of Washington, 
according to report 30 feet of limestone was found directly below 
the coal. Thin sandstone beds also frequently occur in this interval. 
A sample of this limestone from Fayette County was analyzed by 
the Second Geological Survey 6 and found to have the following 
composition : 
Analysis of Fishpot Limestone from Fayette County. 
Sulphur trioxide (S0 3 ) 0. 052 
Phosphoric oxide (P 2 O s ) 066 
Wafer 1.010 
( Jarbonaceous matter. 1. 250 
Insoluble residue 10. 770 
Calcium carbonate (CaC0 3 ) 80. 647 
Magnesium carbonate (MgC0 3 ) .... 2. 217 
Ferrous carbonate (FeC0 3 ) 1. (m? 
Iron disulphide (FeS 2 ) 1 . 125 
Alumina (A1 2 3 ) 543 99. 337 
Compact; minutely crystalline; spotted with pyrite; dark blue. 
If the bed attains this composition in Washington County, it should 
be of some value in the manufacture of Portland cement. One analy- 
sis, however, is not sufficient to justify a positive statement of this 
kind, since another analysis shows too large a proportion of magnesia. 
BENWOOD LIMESTONE. 
The Benwood (or Great) limestone is by far the most important 
limestone in the quadrangle. The name was suggested by I. C. White 
from the town of Benwood, near Wheeling, W. Va. In places it 
reaches, with its interbedded shales, a thickness of 160 feet, the pro- 
portion of limestone being usually about three-fourths of the whole. 
The detailed section of the Benwood varies somewhat, but it consists 
a Bull. U. S. Geol. Survey No. 65, 1891, p. 62. 
b Rept. MM, 1879, p. 287. 
