306 THE JOURNAL OF GEOLOGY. 
case the evidence would be imperfect since the southern bound- 
ary of the state apparently marks the extreme limit to which the 
sea withdrew at the close of the Keokuk epoch. -At several 
localities, however, we have noted a disturbance in the stratifica- 
tion at the base of the arenaceo-magnesian beds which apparently 
represents the break referred to. It is usually marked by a con- 
fused commingling of arenaceous, shaley and calcareous material 
inclosing fragments of chert, broken shells, etc. It appears in 
the Rock Creek section (p. 297) and at several other places in 
Van Buren county, also on East Sugar Creek in Lee county. 
The arenaceous deposits of the arenaceo-magnesian beds are also 
sometimes marked by small quartz pebbles in a more or less 
calcareous matrix, while the cross bedding in the sandstones 
indicate proximity to the shore line or at least shoal water. 
FEET 
Fic. 4.—Section on Bear Creek, Van Buren county (Sec. 10, T. 68, N. R. 9, W.), 
showing unconformity of Lower Coal Measure upon Saint Louis limestone. 
Moreover, the manner in which the Warsaw shales and lime- 
stones below thin out northward offers confirmatory evidence of 
unconformable relations. 
Unconformity above the Saint Lowis—At the close of the Saint 
Louis epoch the sea again receded, evidently quite rapidly, leav- 
ing no enduring evidence of the next succeeding formation 
(Kaskaskia) which lies 100 miles south of the Iowa boundary. 
During the Kaskaskia epoch the Iowa region was subjected to 
extensive erosion, and, on the irregular surface thus formed, the 
Coal Measure formations were subsequently deposited. Expo- 
sures showing this erosion unconformity occur at numerous 
places in southeastern Iowa. Figure 4 represents an exposure 
of this character on Bear Creek. The Coal Measure rocks are 
