E. T. DUM15LE-THE SOILS OF TEXAS. 
27 
mals, have transformed them to greater or less depths into true soils at 
their original place of location, and differing from the subsoils princi¬ 
pally in their greater alteration and the presence of remains of organic 
origin. Such soils are known as Residual, Primitive, or Sedentary soils, 
or soils of disintegration. 
Where water or wind has taken up these materials in suspension or 
solution, transported them to other localities and deposited them, they 
form what are known as transported or derived soils. 
While both classes have a common origin in the rock materials of the 
surface, the former or Residual Soils, being local and dependent on the 
character of the rock immediately underlying them, must differ among 
themselves with every change in its character, while the transported soils, 
being derived from many different localities, but usually thoroughly com¬ 
mingled by the water, are often more homogenous. 
The different soils, then, are due to the different rocks from which they 
are derived. A belt of sandstones will yield a sand}’ soil, a bed of clay 
a clay soil, while a bed of disintegrating limestone may yield either sandy 
or clayey soil in accordance with the impurities contained in the original 
rock. 
If, by a careful study of the geology of a region, we determine the 
locality and extent of the surface exposures of the several beds of clays 
and limestones, sandstones, granites, etc., and carefully plot these upon 
a map, we have a sure index as to what character of soil we may expect 
in any portion of the area so mapped. If to this be added the chemical 
and physical examination of these soils and their interpretation, and 
proper statements regarding the plant growth, drainage, and water sup¬ 
ply, all the data are at hand for forming the most intelligent idea pos¬ 
sible concerning them. A thorough geological survey, which naturally 
includes this, has therefore as great, if indeed it has not a far greater, in¬ 
terest for the farmer than for the miner, the quarry man, or the manu¬ 
facturer. In proof of this it may be stated that it has been fully demon¬ 
strated in France, Belgium, Germany, and Austria, where the improve¬ 
ment of agriculture has received the closest attention, that the only 
sound basis for soil maps are those showing the details of the geological 
formations. 
Since the character and distribution of by far the greater portion of 
the soils is governed by the rock structure of a region, in any system of 
local soil classification the geology must first be understood, and all pos¬ 
sible information obtained regarding the distribution, character, and 
composition of the rock materials. It also follows that the classification 
of the soils can not be more detailed than knowledge of the geology of 
the region will permit. Therefore, in our case, since the work of the 
Geological Survey has only progressed to the determination and mapping 
