522 STUART WELLER 
keta formation. This material can only have been formed as the 
product of the subaerial decay of rocks, doubtless of limestones 
which originally were present above the present uppermost layer of 
the Kimmswick limestone. The deposit is similar in every respect 
to the red residuary clays which are so uniformly present in southern 
Missouri and elsewhere beyond the glacial border, sometimes many 
feet in thickness, and containing the resistant cherts which were 
originally included in the limestone formations now destroyed by 
_ Fic 1—Unconformity between Kimmswick limestone and Maquoketa shale near 
Batchtown, Calhoun Co., Ill. A, Kimmswick limestone; B, Red residuary clay; 
C, Maquoketa shale. 
weathering. The presence of this residuary clay in the section is con- 
clusive evidence of the existence of an area of dry land in the Missis- 
sippi Valley region, probably of long duration, between the period 
of deposition of the subjacent Kimmswick limestone and the super- 
jacent Maquoketa shale. The presence of this bed at this point is 
perhaps only local, but the remarkable fact is that any of this resid- 
uary clay should have been preserved actually in situ. With the 
readvance of the sea it would seem that the wave action would have 
washed the underlying hard rocks clean of their covering, and indeed 
the few inches here present may be only the remnant of a former 
