Indiana Natural Gas Field. — Leverett. 7 
of the borings were obtained from members of gas companies 
in the towns where they were made, and are considered quite 
trustworthy. Some were obtained from well-drillers. Of about 
one-half of the borings no records have been preserved, and it 
was found necessary to rely upon statements made from mem- 
ory either by well-drillers or by members of gas companies. It 
was feared that many errors might exist in a compilation of 
data, of which so large a percentage was acquired in this way 
but our tabulated sheet fails to discover them, — on the con- 
trary it establishes the general reliability of the sections as re- 
ported. In the accompanying tables the divisions are based 
upon broad diiferences in structure. It is probable that by an 
elaborate system of optical and chemical analyses of such 
suits of specimens as have been preserved a good classification 
might be made, comparable in the number of groups represent- 
ed, though perhaps not identical with, the outcropping groups 
which appear in other states between the horizon of the De- 
vonian shales and that of the Trenton limestone. We find 
that such a careful analysis as is called for has not been made. 
A few suits of specimens which have been secured by Dr. A. 
J. Phinney of the U. S. Geol. Survey, have been sufficiently ex- 
amined to satisfy him that several groups not hitherto includ- 
ed in the reports of the Indiana Geological Survey are brought 
to light by these well-drillings. The present status of knowl- 
edge upon this subject is such, however, as to compel us to 
ignore these minor divisions of the "upper limestone" and 
"lower shales" and recognize but three terranes above the 
Trenton limestone, viz. : the "upper shales," the "upper lime- 
stones" and the "lower shales." 
Boundaries of the Devonian shales. — The gas borings 
have demonstrated the fact that in north-eastern Indiana the 
Devonian, or upper shales of our table, extend south scarcely 
far enough to cover DeKalb, Noble, Kosciusko and Marshall 
counties, for at Garrett, Columbia City, Larwill, North Man- 
chester and Rochester the upper rock is the limestone which, 
farther north, underlies the shales. In M^estern Indiana they 
are found to lie entirely west of Logansport, Frankfort, Sheri- 
dan and Indianapolis ; but south of the latitude of Indianapo- 
lis they extend farther east, being struck at Greenwood, Frank- 
lin and Edinburgh in Johnson county. 
