IS Tlie American Geologist Jan. isgo 
has long puzzled the writer, and only lately has the reason 
been discovered. The line of the Balcones is a fracture 
extending across Texas from Mexico to Arkansas. North of 
the Colorado, however, it is concealed by the overlap of the 
Black Prairie, beneath which it extends onward to the 
Ouachita mountains. South of the Colorado it elevates the 
eastern edge of the Grand Prairie, north of that stream it 
elevates the western edge of the Black Prairie. 
The Grand Prairie, whose rocks before the culmination of 
this disturbance dipped sharply eastward, were elevated west 
of it to an almost horizontal position, while the southern 
division of the Black Prairie, at least in places, was lowered 
after the manner of the downthrow of a fault. This line of 
disturbance continues six to ten miles north of Austin, crosses 
into the northern division of the Black Prairie region, which it 
traverses in a direction a little east of north, and slightly 
oblique to the strike, thereby elevating its western edge. 
This disturbance is marked l)y two conspicuous and prob- 
ably associated phenomena. The first and most intimately 
connected of these is a line of springs which find their way to 
the surface through the fault and joints overhanging the line 
of disturbance. The most conspicuous of these are the springs 
of the Leona, the San Pedro springs at San Antonio, which 
are the immediate source of the San Antonio river ; the springs 
at New Braunfels, and the springs of San Marcos. Near Aus- 
tin, the Barton, Mormon, Sieders, and a group of magnificent 
unnamed spring in the bluffs of the river, immediately west 
of the city, mark the line. North of the Colorado the springs 
of Round Rock, Georgetown, Salado, and those southwest of 
Dallas, mark the line. All of these are great gushing streams 
of water bursting suddenly from the rocks, and flowing off in 
large streams, discharging thousands of gallons per hour. 
They. are natural artesian wells made by rents in the rock. 
It is an interesting economic fact that anywhere within a 
few miles of these natural wells, artificial ones can be obtained 
by boring, as has been done at San Antonio, Fort Worth, 
Austin and Waco. 
The Shnmard Knobs. 
The second interesting phenomenon intimately connected 
with this disturbance is a number of laccolitic, possibly vol- 
canic, outcrops, which extend across the state in a line almost 
