52 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
Prairie, Houston count} r , show the character of one of these soils. As 
in all other cases, their fertility depends upon the sources from which they 
were derived, and when, as in this case, they are formed from materials 
rather low in potash and phosphoric acid, and in the process of trans¬ 
portation and deposition these substances are still further depleted by 
solution, we naturally expect to find them lacking in these essential ingre¬ 
dients, and therefore lacking in endurance. 
The drift soil from Williamson county, analysis No. 48, gives still fur¬ 
ther evidence of this fact. Having its origin in the richest materials of 
the black waxy prairies, it possesses all their fertility, so far as mineral 
plant foods are concerned, and being frequently of a somewhat lighter 
character than the original, is therefore more easily tilled. 
46* 
47* 
48+ 
Insoluble matter. 
96..40 
96.75 
80.94 
Soluble silica. 
.12 
.18 
.21 
Potash. 
.06 
.11 
.23 
Soda. 
.41 
• .33 
.20 
Lime. 
.23 
.33 
1.92 
Magnesia. 
Trace. 
Trace. 
.31 
Iron . 
1.07 
.75 
1.92 
Alumina. 
1.13 
Trace. 
2.78 
Phosphoric acid. 
.03 
Trace. 
.07 
Sulphuric acid. 
.08 
.14 
.11 
('arbonic acid. 
.81 
W ater. 
.20 
.36 
2.26 
Organic and volatile. 
1.44 
1.34 
7.89 
101.27 
100.29 
99.55 
* Third Annual Report, Geol. Sur. Tex., p. 23. 
t Third Annual Report, Geol. Sur. Tex., p. 379. 
ALLUVIAL SOILS. 
For a proper understanding of our alluvial soils, a few words are neces¬ 
sary regarding the river systems which have been the vehicles of their 
transportation and deposition. 
A glance at the map will show that the rivers of the State are separa¬ 
ble into the following groups: 
Rivers having their origin outside the State: Canadian, Red, Pecos, 
and Rio Grande. 
Rivers rising in the Central Basin: Trinity, Brazos, Colorado. 
Rivers of the Grand Prairie: Sabine, Neches, Guadalupe and Nueces. 
Rivers of the Reynosa: San Jacinto, Buffalo, Bernard, Lavaca, etc. 
Streams of the Coast Prairies. 
These rivers have each carved its own valley, which varies in width 
with the character of materials through which it has passed and the ero- 
