120 Transactions of the Academy of Science of St. Louts 
by Denham (12). It is similar in accessory minerals to a granite 
in Ste. Genevieve County (47). 
Gray granite cuts the red along Jonca Creek in Ste. Gene- 
vieve County (49) and is found in the vicinity of Syenite. 
Granite porphyry. Granite porphyry, outcropping in the 
Edgehill quadrangle, differs from granite in texture and it has 
a somewhat lighter color than most of the granite. According 
to Tarr (43) the area mapped by Haworth on the south side of 
Mount Devon as granite, is granite porphyry. Tarr (43) also 
mentioned granite porphyry as occurring near the Cornwall 
granite outcrop. The hill east of Wolf Mountain in the gran- 
ite area which is mapped as felsite by Haworth is also granite 
porphyry according to Tarr (43). Haworth (53) describes a 
granite porphyry in the northern end of sec. 11, T. 33 N., R. 5 E. 
Probably other areas of granite porphyry are present and have 
been mapped either as granite or felsite. 
Felsite. Tarr (43) mentions an intrusive, black felsite neat 
the Cornwall outcrop. The writer found evidence of a body of 
intrusive felsite crossing Stouts Creek, west of Ironton and prob- 
ably detailed mapping would show the intrusive nature of a num- 
ber of other bodies of felsite. The highly porphyritic character 
of some of the felsite is suggestive of an intrusive. 
Basic rocks. Small, basic dikes are quite abundant in the 
areas covered by the Iron Mountain and Mine La Motte quad- 
rangle but are not common in other pre-Cambrian outcrops. A 
few occur in the Edgehill quadrangle and have been reported 
as occurring in the Higdon, Coldwater, and Des Arc quadrangles. 
According to Bridge(3), none occur in the Shannon County 
area. Ste, Genevieve County has a number of basic dikes in 
the granite(49). Large masses of basic rock are found in the 
eastern half of the Edgehill quadrangle and the southern half 
of the Mine La Motte quadrangle. 
Composition of the dike rocks is not as variable as texture. 
The dike rocks in the Edgehill quadrangle are composed of gab- 
bro which may contain olivine in addition to plagioclase and 
