IOWA ACADEMY OF SCIENCES. 
33 
more shale than limestone. From 600 to 765 feet occur alter- 
nating dark and light shales with carbonaceous matter scat- 
tered through them. 
The nature of the next sample is such as to place it with 
Devonian limestones as nearly as can be determined, thus mak- 
ing the base of the Kinderhook at the shales already men- 
tioned. The Kinderhook then, is here nearly 270 feet in thick- 
ness. The upper stratum of the Devonian in accordance with 
this conjecture is fine-grained, compact limestone with drab 
shale. This was found at a depth of 800 feet. Below this 
there occurs a series of shales which extend to a depth of 940 
feet. At 810 feet there was a fine-grained, calcareous shale 
follow^ed by darker shale at 850 feet, which showed some indica- 
tions of the presence of limestone. Below this, light- colored^ 
porous shale made its appearance. At 940 feet limestone is 
encountered again. It is coarse, dark and impure; with it are 
pieces of dark shale. The limestone becomes more compact at 
949 feet, and is of two kinds, blue and gray. Numerous crys- 
tals of iron pyrite are scattered through the it. Twenty feet 
lower the formation changes to light shale. 
The limestones which follow seem to be very closely associ- 
ated, being strikingly similar in lithological character. It 
seems better, therefore, to make the base of the Devonian at 
990 feet, with the shale last mentioned. The total thickness of 
the Devonian would thus be nearly 200 feet. No attempt can 
well be made to separate these strata, for there seems to be no 
adecpiate grounds for such a division. It seems best, therefore,., 
to simply refer all to the Devonian and ignore the divisions. 
There next occurs a series of cherty limestones extending 
from 990 feet to 1,200 feet, probably marking the Niagara at 
990 feet. The sample shows coarse-grained, hard, blue lime- 
stone, with a little chert and shale. This passes into a fine- 
grained, compact, white limestone with chert, which continues 
to 1,065 feet where it becomes exceedingly cherty. Intermixed 
with it are also grains of. pure, transparent quartz and rounded 
pebbles of a purer and harder limestone, somewhat darker in 
color. 
At 1,087 feet the limestone is darker, bluish and impure, 
with pieces of chert and flint. A finer-grained, light limestone 
with less chert is disclosed by the next sample at 1,130 feet. 
Forty-five feet below, this gives place to a dolomitic limestone 
