260 
lithographic, and quite often include chert nodules and plates. The upper 
members are the equivalent of the true ‘“‘Cavernous limestone,” and the 
“Barrens.” In the lower portion sinks are not so common, and the strata 
become argillaceous and in many places hydraulic. 
A section through Orange and Washington counties will show the 
following successign of formations: 
Kaskaskia, sandstone— 
St. Louis. Ft. 
Paoli limestone, calcareous shale and lithographic lime- 
SU OTIS Ss 5 Shae oy cc cger che Sepa aire Aiea age Cane aR AI oes pesca 90 
ost River chert) LOSsiPerousiic anes cece ae eerie eens at 
Mitchell limestone, lithographic limestone and calcareous 
shale with chert inclusions, the lower portion argillaceous 
PHANG Meena Co hicch AU EE Od Tarts ct eee ah aati ee Oe. bss 160 
Bedford oodlitiec limestone—Warsaw. .. .. ccs. cece mes ceces 60 
Keokuk. 
FU om x ah ctorea D2 aa! 8 psc elke gseona iehioce aohw an ade cereus Cie cea oRe eae Sail 
The caves of the impure, lower Mitchell limestone stratum are pecu- 
liar in that they are only incidentally connected with surface sinks, and 
generally have streams of water flowing from the external opening. The 
mouth is usually found above the o@litiec limestone in the side hill of a 
deep valley. The interior shows the erosive effects of running water, the 
passage diminishes in size as it recedes from -the mouth, and its side 
branches are low, narrow reproductions of the main cave. To this class 
belong Donnehue’s, Hamer’s and Donnelson’s caves in Lawrence County, 
Clifty and some of the caves near Beck’s Mill, Washington County, and 
nearly all those found elsewhere near the eastern limits of the St. Louis 
group. 
Where the clay shales and argillaceous limestones are the surface 
rocks the country is very much broken by valleys that are quite different 
from the circular and oval depressions of the sinkhole region proper. 
Sinks are not wholly absent, but they are not characteristic. At many 
places the landscape is further modified, and the rock exposure obscured 
by a mantle of Loess clay that is continuous from East White River, 
north of Mitchell, over the odlitiec and eastern argillaceous limestone area 
