176 Foraminiferal Origin^ Etc. — Hill. 
and recrystallization of the calcite of the shells imbedded in 
clays and sands. These beds are always of limited local 
extent and seldom of economic value. The court houses at 
Dallas, Texas, and Washington, Arkansas, are partly con- 
structed of this limestone, but in each case the supply was 
almost exhausted for the building. 
Of the total sediments of the lower Cretaceous formation, 
aggregating over 2000 feet, 1500 feet are limestone (including 
chalk), all but a hundred feet of which are of foraminiferal 
or semi-foraminiferal origin. Of the 700 feet of limestone 
found in the 2100 feet of the upper Cretaceous formation of 
Texas 600 feet are chalks of foraminiferal origin, while less 
than 100 feet are of the laminated near-shore, or of segregatory 
origin. 
The sequence of sediments in each of the two formations 
can be stated as follows : 
The lower Cretaceous subsidence began with the deposition 
of the Trinity sands, which become more and more calcareous 
towards their top. In these sands are occasional beds 
of limestone of laminated or shell brecciate structure. As the 
sea deepened the clays and impure limestones of the basal 
Fredericksburg were deposited, and these were succeeded by 
the deeper sea chalks, a thousand feet or more of which were 
deposited, under conditions so uniform in an ocean so exten- 
sive, and during a time so long, that there is as yet no per- 
ceptible variation in certain horizons throughout its extent 
from Arkansas to Mexico. Succeeding this chalky epoch 
there is an equally extensive deposition of fine greenish clays 
(the Exogyra Arietina clays of Shumard) which may repre- 
sent a slight elevation of the ocean bottom above the chalk- 
making depths, for they in turn are covered by another slight- 
ly deeper lime deposit, whose continuity was destroyed by 
the erosion of the inter-Cretaceous land epoch and the upper 
Cretaceous subsidence. In the upper Cretaceous the transi- 
tion is from Lower Cross Timber littoral sands (Dakota?) to 
the deeper Eagle Ford clays, and from these by becoming 
more and more calcareous to the Austin-Dallas (Niobrara?) 
chalk, Avhose 600 feet or more represents another long con- 
tinued epoch, and from chalk to chalky clays again, — and 
after a long continued epoch of these clays, which make the 
Black lands of Texas, to the glauconitic calcareous sand ; and 
