Reconnoissance soil survey of South Texas Page: 42 of 115
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40 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1909.
of Laredo. Several comparatively small areas cap the divide separating
the Rio Grande and Nueces drainage basins. Many smaller areas
occur within the Zapata fine sandy loam and also in the country
mapped as gravelly soils east of Pato post-office.
Topography.-Being situated principally upon the divide, the surface
is usually rolling to hilly. Some fairly level tracts occur, the one
east of Pato being of this character.
Utilization.-The native growth is chaparral, mesquite, and cactus,
with some grasses. In the wetter years the growth of grass is very
good and furnishes pasture for cattle and sheep. None of it is cultivated,
and owing to topographic position and climatic conditions is
best left to pasture.
A more level topography, absence of or greater depth to the underlying
rock, and a higher agricultural value are the striking features of
this series as compared with the Zapata. The Brennan series is
represented by two members-a loam and a fine sandy loam.a They
are derived from a formation which can probably be correlated with
the Columbia of the Atlantic and Gulf States. While the deposition
of the Pleistocene formation was taking place the Gulf, or the
estuaries of that body of water, extended inward to the western
border of the level coast country. As a result of the less elevation of
the land, the carrying power of the streams to the west was reduced
and their loads deposited. Where erosion had carved out broad
valleys, these deposits were spread out over wide stretches of country
and have given rise to extensive areas of Brennan soils, especially the
fine sandy loam. The eastward extension of this type is undoubtedly
derived from the Pleistocene. The loam seems to be of rather more
recent formation than the fine sandy loam. The largest area of this
type, extending east from McAllen, was influenced, if not deposited,
by the Rio Grande. The Brennan soils are closely related to the
Victoria, but are distinguished from the latter by the darker color
due to the larger amount of organic matter. They may be considered
as the arid equivalent of this series.
BRENNAN FINE SANDY LOAM.
Description.-The soil of the Brennan fine sandy loam consists of a
gray to light-brown fine sandy loam of fairly uniform texture. There
is some variation, however, both as regards the size of the sand grains
and the amount of clay, the type in some places approaching a medium
sandy loam and in others a loam. In some sections the percentage of
a The Laredo silt loam might be considered as a member of this series, but since
it is so closely related to other members of the Laredo series and has been grouped
already with that series it will be discussed in connection with the other Rio Grande
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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/m1/42/: accessed August 17, 2017), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting UNT Libraries Government Documents Department.