Indiana Natural Gas Field.— Lever ett. 
13 
^;=) M& 
5§°'-S^ 
' '^" (M O O lO TI< 
Devonian limestone. — 
Judging from outcrops of 
Devonian limestone in 
Hamilton and southeastern 
Madison county, at Logans- 
port and elsewhere, we con- 
clude that much of Marion, 
Hamilton, Tipton, Clinton, 
Howard, Cass and Carroll 
counties have a limestone 
of this age as the surface 
rock. Examination of a few 
samples from borings in 
these counties confirms us 
in this opinion, but since 
we have no better evidence 
than that derived from a 
hurried inspection of the 
color and texture of rock 
drillings in the places where 
no outcrops occur, it seems 
unwise to attempt a com- 
plete separation from the 
underlying Upper Silurian 
limestone. 
Upper Silurian lime- 
stone-Oyev eastern Indiana 
the prevailing surface rock 
is the Niagara limestone. 
Here and there it has been 
entirely removed by pre- 
glacial erosion, and in 
southeastern Indiana it is 
entirely wanting, the Lower 
Silurian shales forming the 
surface rock. The Niagara 
probably had, previous to 
its erosion, a general thick- 
ness of 300-400 feet. It is 
thicker near the west line 
of its outcrop where the De- 
