GEOLOGY OF OHIO. 
ending with that of Franklin county, comprises one less formation 
than it. 
Marion county, to the northward, has a greater range, by a single for- 
mation—the Niagara limestone occupying a small corner in the north- 
western part of the county, while the Waverly sandstone appears upon 
the eastern boundary. | 
Pickaway county, to the south, and Delaware, to the north, exactly 
agree with Franklin, in both the range and composition of their geolog- 
ical columns. The following formations, named in descending order, are 
found in Franklin county: 
4, Waverly group. 
3. Huron shale. 
2. Corniferous Jimestone, 
1. Lower [Helberberg limestone, or waterlime. 
These formations represent three main divisions of geological time, as 
is shown in the appended diagram : 
Cleveland shale. 
Carboniferous Age—Waverly group Waverly sandstone. 
_ Waverly shales. 
: Huron shales. 
Devonian Age 
Corniferous limestone. 
Upper Silurian Age—Waterlime group. 
These elements will now be briefly described, commencing with the 
lowest: 
1. The Lower Helderberg limestone, or waterlime, is a late-found, but 
important, member of the geological series of Ohio. Its presence in the 
State was first recognized at the beginning of the present Geological Sur- 
vey; but as the structure of the State has been more accurately deter- 
mined, it has been found to occupy a larger area than any other limestone. 
It makes, however, but a very small contribution to the surface of Frank- 
lin county, its outcrops being limited to a few points on Little Darby 
and Big Darby creeks, on the extreme western border. The valleys of 
both these streams now lie in this formation, for several miles above and 
below Georgesville; but, on account of the heavy drift deposits that occur 
here, the rock is seen but at a few points. The best exposure is found 
in the bed and bank of Big Darby, one mile below Georgesville, and in 
the sections formed by small tributaries of the stream in the same 
vicinity. It is also seen in the banks of the Little Darby, one mile 
above Georgesville. The last nanied exposure is a continuation of the 
outcrop below West Jefferson, in Madison county. As both of the local- 
ities named contain the same elements, the description of one will 
answer for both. 
