120 GEOLOGY OF OHIO. 
The Lower Freeport limestone is quite a steady element of the 
scale in the southern portion of the field. Its place is generally 8 to 
10 feet below the coal. It is known as the Lower Buff limestone, and 
is the Snow Fork and Norris limestones of the report in volume ITI. 
The fourth coal above the Ferriferous limestone is the Upper Free- 
port seam. Both coal and limestone are well developed throughout the 
district, the limestone as usual being much steadier than the coal. The 
interval between coal and limestone is reduced to a few feet once more, 
as in the central and eastern portions of the State, and unlike the con- 
dition in the Hocking Valley. 
The coal displays its usual capricious and changeable character. . It 
is workable at a large number of localities, but it does not maintain 
itself from point to point. 
There is in the district one field of unusual promise, comparable to the 
Dell Roy or the Cambridge field, though probably less extended than either 
of these. Itis knownas the Waterloo coal field. A serious error exists in 
my report in volume III, with reference to the Waterloo coal. It was 
identified as the Nelsonville or Sheridan seam. This was an error of 
precisely the same character as that which was made in regard to the 
Dell Roy coal, when it was pronounced No. 6, or the Middle Kittan- 
ning coal. In both cases the location of the seam, so far from the 
margin of the field, furnished an antecedent probability that the seam 
must belong to a higher horizon than the Middle Kittanning coal. In 
the case of the Waterloo coal, there was no error of the general section 
involved, but only an erroneous application of the section. For the 
correction of this error, we are indebted to Mr. Emerson McMillin, of 
Tronton. 
At Olive Furnace, the seam becomes once more for a limited extent 
a blackband horizon. The limestone of the series becomes in many 
cases an ore, sometimes of excellent quality, but generally so uncertain 
in regard to its percentage of iron as to be unfitted for furnace use. 
The Brush Creek coal (Salineville Strip Vein) is a regular member 
of the series. It is No. 7a of the report in volume III. A coaly streak 
occurs quite constantly in the interval between this and the Upper Free- 
port coal, but it does not deserve a place in the list of coals. The Brush 
Creek coal seldom reaches 30 inches in thickness, but its quality is 
generally excellent. There are but few mines opened in it, but its place 
is always recognizable. The Brush Creek limestone (third buff lime- 
