300 THE JOURNAL OF GEOLOGY. 
and are traced with difficulty toward the south. The odlitic 
limestone of Monroe county, Indiana, generally correlated with 
this formation, has been found to occur in an oblong basin or 
trough, pointing to local sedimentation. 
Arenaceous Limestone of the Warsaw.—The arenaceous member 
at the top of the original Warsaw group has evidently been the 
source of much of the confusion in the stratigraphy of this 
region. At Keokuk, it consists of a blue calcareous sandstone 
in a single massive bed eight feet thick. It contains large white 
quartz grains scattered through the finer arenaceous material, 
the whole being firmly cemented by a large amount of calcareous 
matter. Locally, the quartz grains become large enough to be 
called pebbles. With the decrease of the arenaceous element, 
the rock grades gradually through arenaceous to magnesian 
limestone. All of these phases may occur together in alternate 
bands. Asa whole, the rock weathers to a characteristic brown 
from the oxidation of the iron, which takes place more rapidly 
in the arenaceous parts, giving the rock a banded appearance. 
At Sonora quarry, four miles below Nauvoo, this formation is 
well developed. It becomes more shaley toward the north end 
of the quarry and grades horizontally into brown, cellular mag- 
nesian limestone. At the Pontoosac quarries above Niota, IIL. 
the formation has a maximum development of forty feet at one 
point in the quarry, rapidly diminishing away from this locality 
to about fifteen feet. Though having the appearance of a sand- 
stone, and called such, analysis shows it to contain only 7 per 
cent. of sand, a like proportion of clay, and 60 per cent. carbon- 
ate of lime, while the remainder is undetermined, but probably 
consists principally of magnesian carbonate. Cavities lined 
with spar and sometimes containing Millerite, are occasionally 
found in the lower part. In places the arenaceous character is 
replaced by hard, bluish magnesian limestones. The formation 
rests upon blue shale of which thirty-three feet was penetrated 
by drill. The surface of the shale is noticeably irregular and the 
demarkation between it and the formation above is pronounced. 
At Deamude’s quarry, the character of the formation is very sim- 
