Reconnoissance soil survey of South Texas Page: 27 of 115
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RECONNOISSANCE SOIL SURVEY OF SOUTH TEXAS. 25
areas the growing of crops is attended with much uncertainty. Some
small tracts in the valleys might be irrigated by conserving the storm
waters, and under these conditions very handsome yields should be
HOUSTON CLAY LOAM.
Description.-The Houston clay loam consists of a dark-brown to
dark slate-colored clay loam, having an average depth of about 10
inches. The texture becomes heavier and the soil blacker in the
shallow depressions and on the more level areas. Here it approaches
very closely in character the Houston black clay. In the latter areas
the soil sun-cracks, and small mounds and hollows (hog wallows), so
characteristic of the clay, are seen. The surface is usually covered by
a thin baked crust, which has a light grayish appearance. This crust
is especially noticeable on the more rolling areas, where dry conditions
are most pronounced. The upper portion contains enough sand
to give it more of the texture of the surface soil, although lighter in
color. It becomes slightly heavier as the depth increases, and in the
lower part of a 3-foot section changes to a stiff slate or drab-colored
calcareous clay, which is very sticky and tenacious when wet. No
limestone fragments are found in either soil or subsoil, but in some
localities a few rounded gravel are scattered over the surface.
The following table gives the results of mechanical analyses of
samples of the soil and subsoil of the Houston clay loam:
Mechanical analyses of Houston clay loam.
Number. Descrpition. Fine Coarse Medium Fine Very fine Silt. Clay.
gravel, sand. sand. sand. sand.
Per cent. Per cent. Per cent. Per cent. Per cent. Per cent. Per cent.
20785 ............ Soil......... 0.0 0.5 0.3 16.1 24.2 37.6 21.2
20786............. Subsoil ..... .0 .1 .2 12.9 21.5 34.4 30.9
Sample 20785 contained 1.09 per cent of calcium carbonate (CaCOa) and sample 20786, 3.06 per cent.
Origin.-This soil has been derived from the underlying calcareous
clays.a The calcareous nature and rather heavy texture of this
material has been favorable to the accumulation of humus, to which
is due the dark color of the surface soil. The lighter texture of the
surface material has probably resulted from the removal of the finer
particles by the action of both wind and water, although the sand
may have been left in the eroding away of a later and more sandy
formation. Although this type occurs quite frequently in'broad, flat
valleys, it does not seem to have been influenced to any great extent
by recent alluvium, the streams having carved out these valleys in the
a The western area probably represents the Wills Point or Basal clays and the
one east of Encinal the Frio clays.
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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/m1/27/: accessed April 25, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting UNT Libraries Government Documents Department.