Devonian Era in the Ohio Basin. — Claypole. 17 
The palaeontologist notes a marked change in crossing over 
the almost invisible line between Siluria and Devonia. At a 
single step he passes from the dolomitic, and, in Ohio, the 
barren limestones of the Lower Helderberg to the abounding 
life and almost pure calcareous limestones of the Corniferous 
group. A complete palaeozoic break occurs here, but it is 
rather a change from death to life than from one fauna to 
another. The cause of this must be sought outside of the state. 
The Oriskany sandstone of the eastern states there fills the 
gap. 
A. THE CORXIFEROUS LIMESTONE. 
In the absence of the Oriskany, the Corniferous limestone 
is the actual base of the Devonian system in Ohio. It lies as 
a solid floor below all the other groups. Its main outcrop runs 
from north to south, from the lake to the river, as shown in 
map V, and east of this it is continuous over the whole eastern 
part of the state. It has been found in everv drill hole that 
has been pushed far enough to reach its horizon, and to its 
great solidity and to the quantity of chert which it contains 
may be ascribed the sudden stoppage of many of these under- 
takings. 
Aside from this cherty component, the limestone itself does 
not present any special hardness and is usually included by 
the driller with the underlying Lower Helderberg, as 600 feet 
of limestone very hard in the upper part. 
In composition, however, the chemist finds a marked dim- 
inution in the proportion of magnesia and a relative increase 
in that of lime. The rock is no longer a dolomyte but is 
nearer to a normal limestone, as may be seen from the follow- 
ing analyses taken from the "Geology of Ohio.'' 
Lower Helderberg Limestones. Corniferous Limestone. 
Carbonate of Lime 55-97 93-28 Upper. 81.14 Lower 
Carbonate of Magnesia 4427 2.69 16.00 
Silica 1. 41 1.94 
Vol. VI, p. 354- Vol. Ill, p. 936. 
The chert consists for the most part of the casts of fossils, 
especially of corals, in which the lime has been replaced by 
silica during mineralization. Sometimes, as at Bellcfontaine, 
this chert has a chalky texture and appearance, but usually 
it is hard and of various tints from black to white. It was 
