The Pre-Cambrian Structure of Missouri 133 
N. 40° E. and N. 50° W. joints, indicating that the dike is 
older than the jointing. 
Faults. An alignment of topographic feautres extends from 
the northwest corner of the area covered by the Iron Moun- 
tain quadrangle to Grassy Mountain in the southeast corner, and 
may be seen in the boundaries of the igneous outcrops on Plate 
V. At the north end of the quadrangle, the alignment forms 
the east side of the Belleview Valley and the west side of Bu- 
ford Mountain for a distance of about five miles. The line is 
broken for three-quarters of a mile by a side valley that ex- 
tends toward Iron Mountain after which it continues again as 
a saddle across the hill north of Graniteville and passes through 
the valley between Pilot Knob and Shephard Mountain. South 
of Ironton, the valley widens and the alignment becomes in- 
definite. The writer believes that this topographic feature in- 
dicates the presence of a fault line scarp and proposes that the 
fault producing it be called the Ironton fault. 
Another indication of the existence of faulting lies in the 
inclination of the felsite. Near the top of Shephard Moun- 
ih de eo at e, the flow lines dip 12° in the direction 
S. 20° W., while down the slope the dip increases to 50°. Just 
across the valley, the tuff on Pilot Knob has a dip in the same 
direction, Southeast of Ironton at Stouts Creek shut-in, the 
felsites are vertical, 
The difference in lithology on the two sides of the valley 
also suggests faulting, although it could be accounted for on 
the basis of dip. The felsite on Pilot Knob and Cedar Hill is 
red in color and includes some flow breccia. On the hill east 
of Graniteville, the felsite is red and very dense, shows no 
flow lines, and is not very porphyritic. On the other side of the 
valley, the felsite on Shephard Mountain is brownish to purple 
in color and shows very abundant and well-defined flow lines. 
The location of the iron deposits of the Iron Mountain 
quadrangle suggests a structural line. | Nason(33) describes 
ves of ore on Buford Mountain. No iron deposits occur in 
