128 Transactions of the Academy of Science of St. Louis 
Folds. Because of the lack of bedding in the igneous rocks, 
it is difficult to recognize the presence of folding. It is probable 
that folding would be confined to regional tilting and to drag 
along fault planes since igneous rocks are brittle and easily frac- 
tured. Where tuffs are present, it is possible to measure the 
dip, and dip may also be determined where flow lines are pres- 
ent in the felsite. In the case where flow structures occur 
in sheets, the dip and strike can be measured just as in sedi- 
mentary rocks, but where flow structures take the form of 
schlieren it is necessary to measure the pitch of a number hav- 
ing different strikes in order to find the direction giving the 
maximum pitch. Dips may also be measured by mapping the 
contacts of different flows. This can be done only over small 
areas as there is too much variation within a flow to allow cor- 
relation of widely separated outcrops. 
The regional dip seems to be to the southwest which is 
what would be expected because most of the felsite lies on the 
south and east flanks of the St. Francois Mountains. The gen- 
eral dip becomes steeper locally due in part to folding but mostly 
to drag along faults. Without doubt some of the dip in the 
felsite is caused by inclination of the surface on which the lava 
was poured out. 
The dip in the pyroclastics at Pilot Knob is partly a re- 
sult of synclinal structure and partly caused by tilting of the 
syncline (16). According to Tarr (43), intrusion of the gran- 
ite has displaced the felsite causing vertical flow lines in some 
cases. 
Joints(19). Joints in the granite include horizontal and 
vertical sets. 
Horizontal sets, which are well displayed in the quarries 
at Graniteville, parallel the surface and disappear with depth 
suggesting that they owe their origin to relief of pressure on 
erosion of the overlying rock. 
