32 
TRANSACTIONS OF TIIE TEXAS ACADEMY OF SCIENCE. 
cado. These, with the remnantal strip of Cretaceous, divide the basrn into 
four denuded areas. 
The mountain systems include the granite highlands of the Central 
Mineral region, a few remnantal peaks of like character in Greer county, 
and the large mountainous area of Trans-Pecos Texas with its old lake- 
basin valleys. 
Thus it will be seen that the topographic features of the State are 
closely connected with the geological structure and distribution of the 
rock materials. 
It must be borne in mind, however, that climatic conditions have much 
to do both with the formation of a soil and with its fertility, and that 
over so broad an area as that included within our State the differ¬ 
ences of such conditions may always have been, as they are at present, 
very marked. As has been stated, many of these various belts of rock, 
with their resultant soils, stretch entirely across the State from the Sabine 
to the Rio Grande, from a region of copious rainfall to one of frequent 
drouth. Therefore, even if throughout the entire length of any belt 
the mineral composition of the rock material were identically the same, 
there would necessarily be difference in its weathering into soil and in 
the amount of organic matter it contained. 
Residual Soils of the Coastal Slope. 
As will be seen from the accompanying map, nearly one-half of the 
entire State is included in the Coastal Slope. It embraces the region of 
greatest rainfall and many of the most fertile soils. The various belts 
of rock materials which lie within it and which have been briefly men¬ 
tioned in connection with the geology of the region, occur, as has been 
noted, in bands of different widths stretching from the Rio Grande on 
the west to the Sabine or Red River ©n the east, roughly paralleling the 
present Gulf coast, and each one furnishes its own characteristic soils 
and agricultural conditions. 
SOILS OF THE COAST PRAIRIES. 
So lately have the waters of the Gulf and its fringing bays receded 
from that belt of country known as the Coast Prairies, that Loughridge 
applies the term alluvial to all their soils. 
The substructure of this plain consists of limy or sandy clays and 
sands. These were derived from the various beds of older material 
north of them, brought down by rivers and deposited in the ba} r s which 
preceded those of the present. 
The resulting soils, where the sand) deposits prevail and have not been 
