118 Transactions of the Academy of Sctence of St. Louis 
Pre-Cambrian surface under the Paleozoic. Not a great 
deal is known of the pre-Cambrian surface beneath the sedi- 
mentary rocks. However, the outcrops of igneous rocks around 
the borders of the Ozark region in Ste. Genevieve and Camden 
counties in Missouri, and in Mayes County, Oklahoma, indicate 
that the whole area is underlain by a plateau of Pre-Cambrian 
rocks, Though the topography of the exposed pre-Cambrian 
rocks is very rugged, there is no evidence that the surface under 
the Paleozoic formations is equally rugged. Pre-Cambrian ex- 
posures are due to uplifted blocks which were formed during the 
pre-Cambrian. Erosion at the end of the period must have been 
more active in these uplifted areas than in the comparatively 
level areas surrounding them. 
A number of wells in the Missouri Ozarks reach the pre- 
Cambrian. At Sedalia, quartzite is encountered at 1,600 feet, 
which is probably pre-Cambrian as the St. Peter sandstone is 
reached at 360 feet in the same well. At Lebanon, pre-Cambrian 
quartzite occurs at 985 feet, according to Shephard(38), but 
Gould (18) gives the depth as 1,900 feet. The former is prob- 
ably correct as the base of the St. Peter is at the surface and 
it is seldom more than 1,200 feet above the pre-Cambrian in the 
Ozark region. At Sullivan, the pre-Cambrian has been reported 
at 1,200 feet, and near Rolla, at 1,700 feet(51). At Pomona, 
in Howell County, granite was reached at a depth of 2,500 feet. 
Near the western boundary of the state at Carthage, the pre- 
Cambrian lies at a depth of 1,950 feet below the surface. 
Off the Ozark Dome, wells reach the pre-Cambrian along 
the Missouri River Valley. In Jackson County, northeast of 
Kansas City, Missouri, granite is encountered at a depth of 2,400 
feet with the bottom of the well in rocks of Silurian age. The 
pre-Cambrian here is probably lower than in any other part of 
the state due to a synclinal structure in the northwest portion of 
the state. 
PETROLOGY 
Granite. The largest body of granite outcrops in an area 
15 miles long by 10 wide, in the contiguous portions of the Iron 
Mountain and Mine La Motte quadrangles. It has considerable 
