8 
Transactions Texas Academy of Science. 
[ 114 ] 
The materials involved in the faults are much altered and ferruginated 
and along the edges the drag has brought portions of the shale to a per- 
pendicular position, although in the center the beds are almost hori- 
zontal, unless disturbed by later action. Fragments of Washita lime- 
stone are mingled with the shale on the edges of the faults, and the 
materials are streaked with gypsum, while along and near the sides of 
the. faults quantities of dog-tooth spar occur. 
The northwest-southeast fracturing, which followed that of the east- 
west trend, was not accompanied by faulting in this immediate vicinity, 
and the joint planes made by it are ferruginated only to a limited extent 
compared with the others. 
The succeeding dynamic action caused a series of fractures of north- 
south trend, but in this locality the faulting was very slight. Some of 
the fractures, which are ten feet in width, cut entirely and cleanly 
through the east-west breaks and leave the contents of such breaks well 
exposed by the eyosion of the softer filling of those of later date. This 
series of fractures is filled with granular limestone containing stringers 
of calcite and strongly ferruginated. The fractures show distinct slick- 
ensided walls and carry much drg-tooth spar. 
At other places in the area the north-south series of fractures in the 
Fredericksburg limestone frequently show some mineralization, being 
usually filled with oxide of iron and calcite in the form of dog-tooth 
spar. At most localities these vein-like streaks are only a few inches 
in width, but at times they open out to as much as six feet. 
The openings described by Prof. Blake were chiefly in the hills lying 
north of this valley and in them little more than the Washita rocks were 
involved. The deposits, as suggested by him, are in reality both bedded 
and in fissures, and the principal mineralization here appears to be^ along 
the east-west trend, although one of the larger openings was on one of 
the northwest-southeast streaks. 
An interesting structure study was observed in Fresno creek. The 
sedimentary rocks exposed belong principally to the Yola and overlying 
lime shales of the Eagle Ford, capped by a flow of rhyolite (?) of white 
color and well developed columnar structure. 
The lime shales are folded and twisted, dipping in almost every direc- 
tion, and have a number of intrusive sheets or sills of basalt which have 
been forced in along the stratification planes and now appear mterbedded 
with them, occasionally cutting across the 1 strata from a lower to a 
higher plane and less often cutting the shales as dykes. These intru- 
sives are, for the must part, from a few inches to two feet in thickness, 
and simply blacken the shale for a few inches on either side. In the 
upper portion a larger mass, some' 25 or 30 feet in thickness, lies between 
the strata and has metamorphosed both the underlying and the overlying 
rock to a distance equal to its own thickness. 
