124 GEOLOGY OF OHIO. 
Lawrence county is to be referred to this horizon. Its place is about 
50 feet below the Ferriferous limestone, and it is frequently mineable, 
its thickness never exceeding 3 feet, however, so far as known. | 
The probable representative of the Brookville coal is thus seen to 
have a place on the western shore of the coal field. 7 
The Tionesta coal of Pennsylvania seems to be represented in the 
Newland coal of McArthur. This seam in its largest phase is made up 
of two distinct beds, which are separated by 12 to 15 inches of shale. 
The upper portion is often cannel. Further south, two or three coal 
streaks scattered through 15 to 20 feet of shales, hold the same horizon. 
This is No. 36 of my report in volume III. It can be easily identified 
by its relation to the main or upper block ore of the Ohio valley. It 
lies a few feet above this widely-known horizon. 
The Upper Mercer horizon is remarkably distinct throughout the 
entire field, but its chief value lies in the ore which it bears. The lime- 
stone itself, or the flint that replaces it, is found at intervals all along 
the line, but the ore continues where the limestone fails. The ore is 
the now famous Dunkel block ore, or Swan township ore, or Creola 
block ore of Vinton county, the Big Red Block of Jackson county, and 
the Main block ore or Franklin Furnace block ore of Lawrence and 
Scioto counties. 
The coal of this horizon is generally thin, and no considerable 
mines are known in it. 
The interval that separates the Upper and Lower Mercer lime- 
stones varies in different portions of the field. It is 30 to 40 feet in 
Vinton county. It becomes 50 feet or even 60 feet in the lower 
counties. 
The Lower Mercer limestone and its coal and ore are so well 
determined that they require no detailed description here. This horizon, 
next to the Ferriferous limestone, is the easiest to follow, and the 
hardest to lose in the Lower Coal Measures. 
The series that have been thus far described can be more clearly 
shown by arranging the elements in vertical order, and indicating the 
interval that: separate them. 
Ferriferous limestone. 
Coal—Upper Clarion or Scrub Grass, limestone vein. Se 
eet. 
Interval, frequently embracing the Hecla sandstone (from 
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