14 
Transactions Texas Academy of Science. 
[ 60 ] 
The San Marcos river rises in a large spring about one mile northeast 
of the town of San Marcos. An earth-and-wood-and-stone dam, located 
about one-fourth mile below the head, backs the water over the springs. 
The fall at this dam is about twelve feet, and the power is utilized for 
the city water supply and to run the electric light plant, and for irriga- 
tion. The plant is equipped with three 35-inch turbines of the Leif el 
type. The water is pumped into a reservoir 195 feet above the lake. 
Two miles below the head springs is located the dam of J. M. Cape. 
This dam is constructed of frame work and earth, is 130 feet long, with 
a fail of nine feet. The plant is equipped with two 48-inch Leffel tur- 
bines, which under the fall or head develop seventy-eight horse power. 
One-fourth mile below Cape’s gin is located the Thompson gin. The 
race is one-half mile long, and connects to the pond formed by the Cape 
dam. The fall at the Thompson gin is fourteen feet, but to guard 
against the times of low water an auxiliary steam plant of fifty-live horse 
power has been installed. 
About five miles below San Marcos, on the San Marcos river, is 
located the gin and corn mill of J. C. Jones. The dam is constructed of 
cedar timber crib work, filled in with stones, gravel, and concrete. It is 
ninety feet long, seven feet high, and was built in 1896. The power is 
derived from two turbines, one Lelfel-Samson 50-inch diameter, which, 
with the seven feet head obtained, produces ninety-five horse power ; and 
one Lefi'el Standard 23-inch wheel, producing six horse power. The 
power is utilized in operating a cotton gin, corn mill, a small Westing- 
house direct-current dynamo of thirty-five light capacity, and two small 
pumps that are used in supplying water for the irrigation of twenty acres 
of farm land near the mill site. The total cost of the plant, not includ- 
ing the pumps, is $6000. 
About two miles northwest of the town of Martindale, W. S. Smith 
owns and operates a cotton gin and corn mill oh the San Marcos 
river. His dam consists of a central portion of timber frame-work filled 
with rocks and gravel, seven feet high and 200 feet long, and constructed 
by placing alternately pieces of lOxlO-inch cypress timber longitudinally 
and crosswise of the dam and filling in the spaces left between these in 
the rock and gravel. These timbers are not laid flat upon their squared 
faces, but are placed upon edge, and are dapped or let in several inches 
where they cross each other, and are secured by f-incli bolts that extend 
completely through the dam from top to bottom. The lowest course in 
which the timbers lay crossways of the dam rests upon large longitudinal 
logs and extends four feet beyond the toe of the frame work of the dam 
proper. Upon this extension are piled stones of all sizes up to the height 
of the dam, thus forming the down stream face. The top of the frame 
work slopes backwards and upstream to a slight extent, and is sixteen 
feet in width, thus making the dam twenty feet wide at the foundation 
