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26 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1916.
a yellowish or greenish color in the lower part and passes into the
partially decomposed underlying rock at about 3 feet. The soil
is residual from acidic gneiss and schist in which there are small
bodies of granite and dark-colored, more basic igneous rocks. The
topography is rolling, with smooth slopes, becoming rough and
rugged in the areas of stony soil. The land is well drained.
The Brackett series includes soils having a grayish or light!
brownish color at the surface and a grayish or whitish, highly calcareous
subsoil or substratum. In this county the soil color has
mainly resulted from erosion, the original darker colored, residualsoil
accumulations having been removed nearly to the depth of the
underlying substrata of disintegrated chalky limestone or other calcareous
rocks.
The alluvial soils of the county have been correlated in six series,
the Miles, Abilene, Simmons, Frio, Miller, and Bastrop.
The Miles soils are derived from old Pleistocene, and possibly
late Tertiary, fluviatile deposits, spread out as a veneer over old,
high plateau surfaces and occurring also both as broad valley-filling
areas and as terraces along streams. In this county the detritus
composing the alluvium is derived mainly from limestones, with
some influence from sandstones and shales, and has been washed
from the Edwards Plateau and the High Plains. The types of this
series are characterized by a dark reddish brown or dark-brown color
of the soil and a red color in the subsoil. The soils are calcareous
and a tough, calcareous clay hardpan is characteristic of the series.
A whitish or salmon-colored, chalky or marly substratum and hard
calcareous grit, with the character of " mortar beds," are commonly
encountered at depths of 3 to 5 feet.
The Abilene types differ from the Miles in having a slightly darker
color. The surface soils are brown to nearly black and the subsoil
brown. The two series are similar in physiography and origin, the
darker color of the Abilene apparently being due to poorer drainage
conditions.
The Simmons series is similar in origin to the Miles and Abilene,
but comprises soils of still poorer drainage than the Abilene. The soil
material characteristically is black-grayish black at the surface and
slaty black or brownish in the subsoil.
The lower lying alluvial soils along the San Saba River and local
streams where the soil material has been dominantly influenced by
limestones or other calcareous strata are included in the Frio series.
The soils are black or light brown and are characteristically calcareous.
They occupy both recent bottoms and late Pleistocene terraces
subject to occasional overflow.
The Miller series embraces the bottom-land soils along the Colorado
River. The soils have a peculiar chocolate or chocolate-red