The Pre-Cambrian Structure of Missouri 143 
The northwest side of the block is marked by a straight 
northwest—southeast trend of the Big River for a distance of 
over eight miles. The northeast branch of the Palmer fault, 
called the Big River fault, runs along this side for a distance 
of three miles near the northern corner of the block. The cor- 
ner is cut off by the Irondale fault which here trends nearly 
east—west. Immediately south of this fault there are two small 
outcrops of granite which are irregular in shape but elongated 
northeast—southwest, 
The northeast side of the St. Francois Mountains block is 
bounded on the northern end by a continuation of the Irondale 
fault which here turns southeast. Near Doe Run there is a fault 
parallel to it just southwest of the pre-Cambrian boundary. A 
drill-hole near Doe Run passes through a green dike in the 
Bonneterre (44). There are no known faults between Doe Run 
and Mine La Motte to the southeast where the Mine La Motte 
fault runs just ouside the igneous area and parallel to it. At 
this point the edge of the block projects beyond the general boun- 
dary line due to displacement along this fault. 
The southeast side of the block has another area projecting 
beyond the main boundary of the block, and the apparent end 
of this projection is in line with the Ironton fault. Southwest 
of Coldwater, there is an area of granite along the boundary line 
which has already been discussed. A shear zone in the granite 
strikes north—south and is probably due to faulting. The gran- 
ite has been mineralized, the solutions apparently following the 
north—south shear zone. <A basic dike, 20 feet in width, strikes 
. 45° W. and may follow a fault. Southeast of this granite, 
there are two other small outcrops west of Bear Creek. A line 
drawn through these outcrops would pass through the granite 
near Hogan, thus suggesting that the granite lies on a continu- 
ation of the Hogan fault. 
The southwest side of the block is parallel to, and south- 
west of, the Black fault zone. Beyond the fault, the Middle 
Fork of the Black River continues on the same line for ten miles. 
In about the middle of this side of the block there is an indented 
