68 Unwersity Geological Survey of Kansas. 
have reached the top of the Mississippian at distances as great 
as seventy-five feet, implying a very considerable erosion. 
The importance of this question is connected principally 
with a study of shore lines during geologic time. The Mis- 
Sissippian rocks were formed under ocean water. While the 
surfaces were being eroded they were of course above the 
ocean water, and therefore the ocean shore had receded to the 
west. Later, when the Coal Measures were laid down, covering 
eroded surfaces, the shore lines again migrated eastward. If, 
during the erosion period, the shore line migrated very far to 
the west the eroded area likewise will extend farther west. 
But if, on the other hand, the eroded area forms a narrow 
stretch extending along the southeastern limit of the Coal 
Measures as we now find them, then the shore line immediately 
previous to Coal Measure time did not progress very far to 
the west. This latter condition seems to have prevailed. 
The extent of erosion in Kansas, as far as is known, is not 
very great, and therefore does not imply a very long period be- 
tween Subcarboniferous and Coal Measure time. There is a 
perfect conformity between the Coal Measure strata and the 
upper surface of the Mississippian in Kansas when viewed 
over wide areas, as is clearly shown by the geologic sections 
published in this report; but locally there are many lesser ex- 
amples of nonconformity on a small scale, produced largely by 
an interperiod of erosion rather than by a marked difference 
in positions of bedding-plains of the Mississippian and Penn- 
sylvanian. If, therefore, there were any considerable oscilla- 
tions after the Mississippian limestones were formed and pre- 
vious to Coal Measure time it is remarkable that the final state 
of equilibrium reached and maintained during the earlier part 
of Coal Measure time should place the surface of the Missis- 
sippian in a position so that no broad nonconformities should 
be produced. These conditions indicate, therefore, that the 
oscillations which resulted in leaving the Mississippian rocks 
above the sea and in again depressing them so they could be 
covered by Coal Measure strata were confined to slight vertical 
movements and to narrow limits along the coastal area, move- 
ments which did not materially affect the same rocks further 
oceanward. ~ 
