152 Transactions of the Academy of Science of St. Louis 
GEOGRAPHY AND GEOLOGY 
The area investigated during the 1939-1940 field season was 
the central and southeastern portions of Jefferson County, the 
northern boundary of which is St. Louis County. The eastern 
boundary of the county lies along the Mississippi River and the 
western boundary of the county is Franklin and Washington 
counties. Ste. Genevieve County and a tip of St. Francois 
County lie to the south. 
Jefferson County is very hilly being a part of the Ozark 
foothills. Long lines of ridges extend in a general east to west 
direction. These hills are often forested except where too pre 
cipitous for vegetation or where cleared for farming. Besides 
the Mississippi River which serves as an eastern boundary for 
the county, the Meramec bounds the N.E. and N.W. sections 
of the county while the meandering Big River runs from south 
to north near the western edge of the county. Several tributary 
streams have their headwaters in Jefferson County and flow 
directly into the Mississippi. The most important south of the 
Meramec are Rock Creek, Glaize Creek, Sandy and Joachim 
Creeks and the Isle du Bois at the southeastern edge of the 
county. Bottomland is restricted to the tributary streams. There 
is very little bottomland along the Mississippi River itself be- 
cause the channel lies against limestone bluffs. 
Jefferson County lies on the northeastern flank of the Ozark 
dome. The rocks follow the dip of the area which is about three 
degrees to the northeast. There is considerable minor faulting 
and in the extreme southwest there is faulting of major prcpot” 
tions. The southwestern two-thirds of the county consists of 
rocks of Canadian and older age. From Festus to Kimmswick 
and inland ten miles from the Mississippi are rock exposures 
of the Ordovician series including the Everton, St. Peter, Joa- 
chim, Plattin, Decorah, Kimmswick, Fernvale and Maquoketa, 
with patches of the Mississippian or residual chert on the higher 
hills. North of Kimmswick the country rock is mostly Lower 
and Middle Mississippian rock of Glen Park, Bushberg, Fet™ 
Glen, Burlington, Keokuk, Warsaw and Spergen. There is 10 
Silurian or Devonian rock which must have completely eroded. 
