SUPPLEMENTAL REPORT—HANGING ROCK DISTRICT. 895 
Coal Measures. It can be followed without the slightest uncertainty 
from the Ohio Valley as far at least as Bristol, Perry county. 
4, Shawnee Limestone—The. Shawnee, or Buff Limestone, is the next 
of the main series to be reached in ascending the scale. Its average 
elevation above the Gray Limestone in the Hocking Valley is one hun- 
dred and ten feet, but the distance increases somewhat to the southward, 
becoming ong hundred and thirty or one hundred and forty feet in Law- 
rence county. ‘nis limestone is a persistent, though not very conspicu- 
ous member of the geological scale of the Hanging Rock District. It 
takes its name from Shawnee, Perry county, where it is extensively 
worked for furnace flux. It is also largely worked for the same pur- 
pose in the Monday Creek and Snow Fork valleys. Its thickness 
varies between one and three feet, but it falls below two feet much 
oftener than it rises above this measure. 
Its color is described by the name by which it is generally known, 
viz., the Buff Limestone. The best varieties of it carry ninety-thres per 
cent. of carbonate of lime and only four or five per cant. of silica, but it gen- 
ally contains ten or fifteen per cent. of silicious matter and not more than 
eighty to eighty-five per cent. of carbonate of lime. The amount of iron 
and alumina often rises to ten or fifteen per cent. and a small percentage 
of manganese is a constant element. The best varieties of it are not 
surpassed in purity by any limestone in the district, but it is unsteady 
In compositioa. It is commonly called non-fossiliferous, as it lacks the 
usual coal measure forms, but fragments of crustaceans are not of rare 
occurrence init. It never passes into flint, as the limestones previously 
described so often do. On the whole, it is an excellent and reliable guide 
to the geology of the district to which it belongs. The only uncertainty 
in regard to it that is likely to occur, results from a duplication of 
this portion of the series in some parts of the district. From twelve to 
twenty feet above the Shawnee Limestone, and about the same distance 
below, two other Buff Limestones are sometimes found, but they are of 
more interest as ore beds than as limestones, and will be treated on a 
subsequent page under that head. | 
5. The Cambridge Limestone.—The fifth member of this orderly series 
of limestones is the stretum called the Cambridge Limestone by 
Prof. Andrews. The name is derived from the village of Cambridge, 
Guernsey county, where this limestone is said to be well developed. 
The Cambridge Limestone has long been recognized as one of the most 
persistent of our Coal Measure limestones. It stretches through every 
county of Ohio in which its proper horizon is reached, and furnishes an 
invaluable guide in the determination of the order of the Lower and the 
Barren Coal Measures. The geologists of the first survey caw its avail- 
