The Pre-Cambrian Structure of Missouri 137 
the black porphyry is an intrusion into the flow breccia, the iso- 
lated mass of breccia might be a roof pendant or downstoped 
block. No contacts between the black and red porphyry and the 
purple flow breccia were found. On the northwest side of the 
ridge, fragments of a red porphyry are included in the purple 
flow breccia. Across the valley to the northwest, the flow brec- 
Cia is red with purple fragments and, close to the granite, the 
breccia becomes entirely red. 
A pink rhyolite crosses Stouts Creek at the west end of 
the shut-in, just west of the bridge. This felsite forms a band 
350 feet wide which runs the length of the hill to the south 
of the shut-in. It may be traced up the slope to the north of 
Highway 70 across the hill and down again to the road. Flow 
lines are roughly parallel to the borders of the body of rhyolite. 
The contact between the pink rhyolite and the black and red 
porphyry is well exposed on the hillside north of the road above 
the east end of the bridge over Stouts Creek. It is vertical and 
very sharp, indicating the pink rhyolite was intruded after the 
black and red porphyry had completely cooled. Quartz pheno- 
crysts are abundant in the pink rhyolite close to the contact, but 
disappear 15 feet from it. 
There are two exposures of a fine-grained, red granite north 
of the shut-in on the west side of the ridge which are apparent- 
ly intrusions in the felsite. Although the contact was not seen, 
typical felsite occurs 20 feet from typical granite indicating that 
the contact is fairly distinct. Apparently there is gradation be- 
tween the felsite and the granite because of recrystalization of 
the felsite by the intrusion of the granite. Tarr (43) cited this 
locality as an example of the intrusive relationship of the gran- 
ite to the felsite and stated that the felsite had been recrys- 
talized. The fact that there is more recrystalization at this 
locality than there is near granite contacts in other localities in- 
dicates that the felsite here was still hot when the granite was 
intruded. The close relation of the two intrusions is shown 
by the fact that they are similar in composition and both con- 
tain abundant masses of specularite. 
