The Pre-Cambrian Structure of Missouri 141 
OzARK DoME 
The Ozark Dome is an uplifted area occupying the south- 
ern half of Missouri and extending into northern Arkansas and 
eastern Oklahoma. The two main periods of movement are 
shown by the major structures which are the Springfield anti- 
cline and the northwest trending folds and faults with underly- 
ing pre-Cambrian fault blocks. The difference in age between 
these structures is brought out by the difference in trend of 
the Ordovician-Mississippian and Mississippian-Pennsylvanian 
contacts in the southwestern part of the dome. The Springfield 
anticline is the present axis of uplift. In addition to the fold- 
ing and faulting there have been repeated uplifts of the dome 
as a whole, as shown by the numerous unconformities through- 
out the stratigraphic section. 
The boundary of the uplift on the east side is quite sharp. 
East of the St. Francois Mountains the Paleozoic rocks all dip 
to the east and faulting which has already been described, occurs 
there. The boundary is marked by the Ordovician-Mississip- 
Pian contact through St. Louis and Jefferson counties, by the 
Mississippi River from Crystal City to a point north of Witten- 
berg, and by the fault zone from McBride, Missouri, to the 
edge of the Gulf Embayment in southern Illinois. The boun- 
dary as a whole is quite straight and trends N. 50° W., parallel 
to the strike of pre-Cambrian faults. 
The southeastern boundary of the uplift is marked by the 
border of the Gulf Embayment as far as Batesville, Arkansas. 
The straightness and southwest trend of the border of the em- 
bayment suggest an underlying pre-Cambrian fault. From 
Batesville, the boundary of the Ozark Dome strikes west into 
Oklahoma. The southwestern end of the Ozarks, in Oklahoma, 
is marked by a number of normal faults which are roughly par- 
allel to the Springfield anticline. 
The northwest boundary of the Ozark Dome is not as sharp 
as the boundaries on the other sides. The Pennsylvanian-Mis- 
Sippian contact trends northeast from the northeast corner of 
