Reconnoissance soil survey of South Texas Page: 25 of 115
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RECONNOISSANCE SOIL SURVEY OF SOUTH TEXAS. 23
nearly similar that identical soils have resulted. These soils occur
almost entirely north of the divide between the Nueces River and
the Rio Grande, although a few small areas usually too small to be
shown on the map occur south of this ridge.
Differences in the percentage of sand in the underlying clays, combined
with the influence of the wind in removing the finer particles
from the surface material, as well as drifting it in from more sandy
formations, have given rise to variations in the texture of the soil, so
that two types in the Houston series have been recognized-a loam
and a clay loam. The two are usually very closely associated, and
a detailed separation was impracticable. Therefore areas shown on
the map as one type often represent simply the predominance of
that kind of soil.
While these soils have been included in the Houston series it is
recognized that the drier climate here has caused them to be more
calcareous and to contain less humus than is usually the case in the
corresponding members mapped in areas farther east. The native
vegetation also partakes more of the character of that of the arid
region, the larger percentage of cactus and mesquite being very
noticeable. However, as these soils represent the southwestward
extension of the black prairie region and soon grade into the typical
soils of this belt north of here, it has seemed best to include them in
Description.--The Houston loam consists of a light to dark brown
or dark-gray loam, varying in depth from 8 to 18 inches. The dry
condition of the soil has permitted the removal of the finer material
from the immediate surface, leaving the sand, thus causing the
texture sometimes to approach a fine sandy loam. This is especially
true immediately adjacent to the divide in Duval County, which is
capped by sandstones. -Here the sand from the weathering of these
rocks, as well as from other sandy areas, has given the soil a lighter
texture. This is more or less the case wherever the type adjoins
more sandy soils. The lighter texture is usually found upon the
summits of the low hills or ridges, where the percentage of sand may
become sufficient to approach a heavy fine sandy loam. The soil
contains considerable humus, which gives it a rather dark color and
makes it friable and easily cultivated. The color is somewhat darker
in the eastern than in the western part of the area, and the surface is
often covered by a thin crust, which causes it to have an apparently
much lighter color. This darkening from organic matter extends
to an average depth of about 10 inches, where there is a gradual
change into the subsoil.
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Coffey, George Nelson. Reconnoissance soil survey of South Texas, book, June 16, 1910; Washington D.C.. (texashistory.unt.edu/ark:/67531/metapth19753/m1/25/: accessed July 21, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting UNT Libraries Government Documents Department.