History of Texas, Together with a Biographical History of Milam, Williamson, Bastrop, Travis, Lee and Burleson Counties. Page: 156

iASTOkY OF TEXAS.

This would, therefore, in its widest application,
embrace even the addition of sands to
clay soils of such sticky character as our
famous black waxy. The deposits, however,
which will be mentioned here are apatite,
bat guano, gypsum, glaucohite (or greensand
marl), chalk marl, limes and clays.
Apatite, which is a phosphate of lime, has
as yet been found only in very small quantities
in Texas. Its value as a fertilizer is due
to its contents of phosphoric acid, and if it
can be discovered in any quantity will be of
very considerable value in connection with
the greensand and other marls in sandy
lands low in that essential element. Phosphate
of lime is also the chief constituent of
bone, and any deposits of this character will
also prove of value. As yet known, no deposits
rich in phosphatic material have been
found in Texas.
Bat guano, as a fertilizer, occupies a place
second to nothing, except it be the Peruvian
guano. Its great value as a fertilizer is due
to its salts of ammonia, potash and phosphorus.
It is found in caves in Williamson,
Burnet, Lampasas, Llano, Gillespie, Blanco,
Bexar and other counties of Texas in great
quantities. It varies greatly in quality.
Many of the caves are so situated that water
has access to the beds, and parts of the
valuable salts of ammonia are dissolved and
carried off. In others, fires have by some
means got started and immense bodies of the
guano burned. Many analyses have been
made from different caves, and large quantities
of it have been shipped, but the present
lack of railroad facilities in the vicinity
of the deposits has prevented their successful
working.
Analyses of guano from Burnet and Gillespie
counties gave a value of ovfr $50 per
ton.

Gypsum, as a top dressing for many crops,
is of great use, and when ground for this
purpose is known as land plaster. Ground
gypsum is also an excellent deodorizer.
Texas is abundantly supplied with this
material. Not only does it occur in immense
deposits in the Perniian beds west of the
the Abilene-Witchita country, but all through
the timber belt beds it is found along the
streams and scattered through the clays as
crystals of clear selenite, often miscalled
(* mica " or " isinglass." It is of all degrees
of purity, from the pure selenite to an impure
gypseous clay. So far it has been little
used for this purpose in Texas.
Green8and marl is a mixture of sand and
clay with greensand, and often contains
quantities of shells. Greensand, or glauconite,
as it is often called, is a mineral of green
color composed of silica (sand) in chemical
combination with iron and potash, and usually
contains more or less phosphoric acid,
and the shells furnish lime. Where it occurs
in its original and unaltered condition it is
is of a more or less pronounced green color,
due to the color of the greensand in it.
Where it has been subjected to chemical
action the greeusand is gradually decomposed
and the iron unites and forms hydrous
oxide of iron, or iron rust. This alteration
gives rise to a great variety of color in the
different beds of the material, When it is
fully altered in this way it forms the red or
yellow sandstone so much used in east Texas.
Numerous analyses have been made of
these marls, both in their original and
altered conditions. They contain, in all the
samples tested at least, lime, potash and
phosphoric acid, just the elements that are'
required to fertilize the sandy soils and to
renew and increase the fertility of those that
have been worn out. These elements occur

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