84 
IOWA ACADEMY OF SCIENCES. 
with some chert and dark shale. This extends to a depth of 
1,200 feet. 
At this point the nature of the strata seems to change 
entirely, the limestone giving place to a series of shales, which 
from their position may properly be referred to the Maquoketa 
shales, thus marking the base of the Niagara at 1,203 feet. 
These shales are light- colored and interbedded with thin layers 
of limestone. Carbonaceous matter was also intermixed with 
the shale and limestone. This formation can not be far from 
150 feet in thickness. 
The sample taken at 1,320 feet shows the nature of the strata 
to have changed again. It is a fine-grained, brown, arenaceous 
limestone, containing a large amount of iron and magnesium. 
Lower down it becomes coarser, and at 1,380 feet it gives place 
to dark shale which continues for twenty feet. From 1,400 feet 
to 1,475 feet there occurs a fine-grained limestone decidedly 
dolomitic and very ferruginous. Unfortunately there is no 
record of the strata between 1,475 feet and 1,610 feet. A drill 
was lost and in attempting to pass it the samples were forgot- 
ten. The dolomitic character of the limestone between 1,320 
feet and 1,475 feet would seem to indicate that they belong to 
the Galena group. If so, then the contact between this and the 
Trenton is in the gap between 1,475 feet and 1,610 feet. 
The first sample of what is called the Trenton resembles fer- 
ruginous sandstone, but is in reality fine-grained, highly fer- 
ruginous dolomite with small pieces of white chalky matter, 
nearly pure carbonate of lime. This continued through 1,625 
feet, becoming less ferruginous, and gave j)lace at 1,630 feet to 
coarse, impure white limestone. At 1,640 feet a piece of blue 
shale about two inches long was brought up with the drillings. 
This was filled with fragments of the shells of brachiopods and 
pieces of bryzyoans. There were also numerous crystals of 
pyrite scattered through it. Fifteen feet lower, at 1,655 feet, 
the drillings disclosed a layer of dark, impure ferruginous lime- 
stone, also dolomitic. 
This is considered to be the base of the Trenton group, for 
the next sample taken at 1,700 feet is gray, slightly calcareous 
sandstone, becoming lighter-colored, and more nearly pure at 1, 740 
feet. This evidently represents the Saint Peters sandstone. 
Here, between 1,740 feet and 2,002 feet there is another gap in 
the record. As the drill was penetrating the sandstone a roar- 
ing sound was heard, and the drillings were washed away by a 
