The Pre-Cambrian Structure of Missouri 123 
Intrusion of granite porphyry—on the Edgehill, Mine La Motte, 
and Higdon quadrangles. i 
Iron deposits formed—at Pilot Knob, Iron Mountain, Shephard 
Mountain, Cedar Hill, Shut-in Mountain, and Buford 
Mountain. 
Intrusion of fine-grained red granite 
of Hogan. 
Intrusion of red felsite—east of Ironton. 
Faulting—Iron, Munger, and Hogan faults. 
Intrusion of basic dikes—main dikes of Iron Mountain and Mine 
La Motte quadrangles. 
Intrusion of Silver Mine granite—along southern border of main 
mass Of granite. 
Intrusion of diabase—at Skrainka, Tin Mountain, and in the 
Edgehill quadrangle. 
Intrusion of fine-grained brown granite—-at Skrainka and Jonca 
east of Ironton and west 
re 
Extrusion of felsite—throughout the St. Francois Mountains and 
Shannon County areas. 
Part of the evidence for the above sequence is based on 
structure and will be discussed more fully later. All of the in- 
trusions are later than the felsites which they intrude. Denham 
(12) found evidence that the fine-grained, brown granite was in- 
truded by the diabase. The relation of the diabase to the Sil- 
ver Mine granite is not known but the Silver Mine granite is 
intruded by the basic dikes striking northeast and is therefore 
older, 
The early basic dikes are probably earlier than the faulting 
inasmuch as the majority trend at right angles to it, while later 
dikes are parallel to it. Faulting preceded the intrusions east of 
Ironton, since they seem to parallel the fault surface. It is also 
earlier than the Graniteville granite because the granite lies 
across two faults and is not displaced. ‘The intrusions east of 
Ironton consist of granite intruded into rhyolite which in turn 
is intruded into felsite. Both the granite and the intrusive rhyo- 
lite contain abundant specularite and pyrite. This suggests that 
the iron ores were introduced with the granite and intrusive 
