150 Transactions of the Academy of Science of St. Louis 
Graniteville granite and larger ones might well occur in other 
pre-Cambrian rocks. The Decaturville Dome is part of an up- 
lift too large to be explained by the intrusion of a dike. Dips 
of the sedimentary rocks around the dome may be explained 
in part by initial dip and in part by later elevation of the pre- 
Cambrian surface. That there has been the latter movement 
is shown by the presence of a fault to the northwest, as shown 
on Plate VIII. Silicification of the limestone in contact with 
the pegmatite may be due to groundwater following the contact. 
Shephard (39) recognizes the fact that the Decaturville 
Dome is part of a much larger uplift, and states that the Paleo- 
zoic rocks increase in elevation from Greene County towards 
the dome. This larger uplift is outlined by the contact of the 
Roubidoux and Jefferson City formations as shown on Plate 
VIII. While the area is elongated northeast—southwest, it is 
made up of a series of northwest—southeast trending folds. The 
main axis is the Proctor anticline which extends from the Ben- 
ton County line, through Morgan into Camden County. The 
Osage River follows this alignment for nearly five miles with 
Linn Creek continuing along this same line for a nearly equal 
distance south of the river. 
Parallel to the Proctor anticline and to the west of it, an 
anticline extends from Hahatonka across the Osage River. From 
the Niangua River to Hahatonka there is a fault immediately 
west of the anticline. South of Hahatonka, Spencer Creek con- 
tinues on this northwest—southeast structural axis nearly to De- 
caturville where it turns northeast. The axis of the Decaturville 
Dome strikes northeast—southwest across the line. South of the 
dome, the northwest—southeast alignment is continued by Dry 
Auxglaixe Creek for about seven miles. This trend probably rep- 
resents a pre-Cambrian fault along which there has been later 
movement. Displacement along the fault in the Paleozoic rocks 
has been too small to account for the elevation of the pegma- 
tite at Decaturville. Although the Decaturville Dome appears 
to be on the downthrown side of the fault plane, it probably 
represents a projection along the edge of a pre-Cambrian block 
similar to those seen on the Avon block. 
