14 Bulletin of Labomtories of Denhon University [voi. xi. 
ures suggest that the surface of the rock in that locality is gent- 
ly undulating. 
Below the corniferous lies the Lower Helderberg or Water 
Lime, a great series of beds having a maximum thickness of 
600 feet. Above the Corniferous the Hamilton is doubtfully 
found. This is succeeded by the Ohio Shale which attains a 
thickness ranging from 250 to 3,000 feet. 
CHEMICAL CONSTITUTION. 
The formation is almost always limestone. The only ex- 
ceptions are the thin intercalated layers of sandstone found at 
West Jefferson and a few other points, and the shaly layers 
lying above the bone-bed at Columbus and other places. These 
shales, however, are calcareous. The Upper or Delaware beds 
are less pure than the Lower beds, and contain more iron, 
alumina, and silica. The average may be taken at 75 % car- 
bonate of lime and 25 % carbonate of magnesia. The magne- 
sia increases as the underlying Lower Helderberg rocks are ap- 
proached and decreases as the top of the formation is reached. 
Some of the lower beds contain as much as 35 ^ carbonate of 
magnesia, while the top layers may contain 2 ^ only. 
The carbonate of lime in the upper Columbus beds reaches 
95 while in the highest layers at Kelley’s Island it exceeds 
97 %•* * 
Scattered through the beds are nodules of chert. These 
sometimes are almost wanting, as at Kelley’s Island. At Co- 
lumbus they form several irregular bands. In France’s quarry, 
Bloomville, there is a series of beds aggregating 18 feet in 
thickness in which the chert composes 25 % (estimated) of the 
rock. 
THICKNESS. 
The maximum thickness of the Corniferous rocks of Ohio 
* f so far as present records show, is between 75 and 100 feet. 
^ Edward Orton, Geol. Surv. of Ohio, Vol. VI, page 753. 
* Oeol.-Sury. of Ohio, VII, page i8. 
