28 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
of the broader features of our geologic structure, we must content our¬ 
selves with equally broad classification of the soils which they produce, 
and leave the more detailed work for the future. 
It must therefore be understood that the following statements and 
classification are very general, and preliminary to a more detailed study 
of each bed and soils resulting therefrom, and subject to rearrangement 
and correction as the work progresses. The geological work on which 
it is based was done principally by the Geological Survey of Texas. The 
analyses and descriptions of the soils made use of are those of Dr. Lough- 
ridge in “Cotton Production” in the Tenth Census Reports, Prof. H. H. 
Harrington, of the Agricultural and Mechanical College of Texas, and 
others, appearing in the Survey Reports or existing in its records. 
In presenting this paper, it is simply proposed to place the classifica¬ 
tion on its true basis and as far as may be to lay the foundation on which 
other workers may hereafter rear a complete structure. To do this a 
glance at the geology of the State is necessary. 
Geology. 
The geological development of the broad area we call Texas had its 
beginnings, according to present evidence, in what are now the granite 
highlands of Llano and Burnet counties and in El Paso county. Of the 
early history of the more western portion we can say very little at pres¬ 
ent, but from the exposures of the central area a fairly well connected 
history can be made out, although it is very incomplete in detail. 
In very early times the rocks of this granitic core formed an island or, 
more probably, a headland extending southward from a similar area in 
Indian Territory, and possibly connected in some way with the older 
granites of El Paso county. These rocks were subjected to strong earth- 
movements, which crumpled them into great folds and made fissures in 
them, into which were forced the molten rocks from below. The surface 
was. acted on by atmospheric forces and by the waves of the surrounding 
ocean, and the materials derived in this way from the land were deposited 
in its waters as a series of broadening fringes, interrupted or assisted at 
various times by the operation of volcanic forces. This gradual growth 
continued until the beginning of the Coal Period, at which time the cen¬ 
tral core had an area at least approximating that of our Central Mineral 
Region, comprising Llano county and parts of Burnet, San Saba, McCul¬ 
loch, Mason, Gillespie, and Blanco. During the same time rocks of sim¬ 
ilar character were being formed in our Trans-Pecos area, where they now 
appear as detached mountain masses or long lines of beetling cliffs in El 
Paso and Presidio counties. Up to this time the rocks are composed, 
