The Pre-Cambrian Structure 
of Missouri 
Howarp B. Graves, JR. 
Introduction 
GENERAL STATEMENT 
Little previous work has been done on the structure of the 
pre-Cambrian rocks of Missouri. Inasmuch as faults in the 
Paleozoic rocks extend to the pre-Cambrian area on the east 
and north, it seemed probable that they might extend into the 
Pre-Cambrian. It also seemed likely that some of the Paleo- 
zoic structures were due to movement along pre-Cambrian fault 
planes. This investigation was therefore undertaken with the 
intention of locating as many pre-Cambrian structures as pos- 
sible and relating them to later structures. It was hoped that 
the structures found could be correlated with those in pre-Cam- 
brian rocks of other regions and something learned of the na- 
ture of the forces which produced them. 
Discussion of the pre-Cambrian of Missouri is based on 
field work done in the summers of 1933 to 1936. The strike of 
jomts was determined in nearly 100 localities in the St. Fran- 
cois Mountains by measuring from 10 to 100 joints in a given 
locality, the number depending on their regularity. The geology 
of Several small areas was mapped in order to determine the re- 
lation of the distribution of various rocks to structures. The dis- 
Cussion of structures occurring in rocks younger than pre-Cam- 
brian is based largely on the work of others as recorded in the 
literature, 
