160 Transactions of the Academy of Science of St. Louis 
to the N. 40° E. set. Joints striking N. 80° E. may belong to 
the N. 70° E. set or to the E—W. set. The Springfield anti- 
cline strikes about N. 70° E. and it is possible that the joints 
originated with the anticline during the Tertiary, as there is 
no definite proof they are pre-Cambrian. 
SOURCE OF STRESS 
The possible sources of the stress forming the joints and 
faults in the pre-Cambrian rocks include igneous intrusion, ver- 
tical uplift, and horizontal compression. While the minor sets 
of joints may be the result of intrusion, the major structural 
systems are too widespread to have been formed by anything but 
major crustal movements. Vertical uplift would produce struc- 
tures that were unoriented or were radial or tangential to the 
uplift but structures throughout the state have the same trends 
indicating horizontal compression over a wide area. 
During pre-Cambrian time there were two structural sys- 
tems developed which were of regional origin. The N W. 
‘and the N. 40° E. system is dominant in Missouri and im- 
portant in the Llano region of Texas. The N. 70° W. and N. 
20° E. system is dominant in the pre-Cambrian of the Wichita 
Missouri. These systems were developed as a result of com- 
pression from the southwest from two somewhat different di- 
rections at different times during the pre-Cambrian. The stress 
must have originated at a considerable distance southwest of 
any of the pre-Cambrian localities and probably came from the 
Pacific Ocean basin. 
Joints not belonging to either of the above systems may 
be of local origin or in the case of the N.—S. and E.—W. sets 
may be due to a minor, but regional, movement. Many of the 
joints in the pre-Cambrian rocks may be due to movement at 
a later time but it seems more probable to consider them all 
of pre-Cambrian age. Until the age relations of the various 
pre-Cambrian rocks have been definitely worked out, it is im- 
possible to determine the relative ages of the different sets of 
joints. 
