HAYES AND 
KENNEDY. 
GEOLOGY OF EASTERN DIVISION. 23 
composition and texture. The beds as exposed along the Frio River 
are a series of gypseous clays with sand and sand rock. a Between 
the Brazos and Trinity rivers the beds are grayish sandy clays with 
nodular concretions of lime and occasional deposits of gypsum crys- 
tals, thin strata of sandstone, and bluish-gray sands containing 
nodules of lime and clay. East of the Trinity the calcareous clay 
beds become predominant and the sandstones are never very strongly 
represented, losing their continuity of stratification and appearing 
simply as large concretions or bowlders. Another peculiarity in the 
Frio beds, which appears more prominently in the eastern division than 
in the other sections, is that when they are thin bedded the calcareous 
concretions are largely replaced by crystals of gypsum, while where 
they are thick bedded gypsum crystals do not occur and calcareous 
concretions are found exclusively. 
There has been considerable disagreement as to the age of these 
clays. Hilgard, Hopkins, and Loughridge assigned them to the Grand 
Gulf and considered them as of Miocene age, and lately Harris has 
been inclined to consider them as Grand Gulf but belonging to the 
Oligocene. The Texas geological survey held them to be of Eocene 
age and placed them at the top of the Eocene column. They have 
been assigned to that portion on account of their containing fauna 
which appears to be distinctly of Eocene age. 
BURIED BEDS. 
The next succeeding beds do not outcrop, and their existence has 
been demonstrated by drilling. These are the beds marked b, c, and 
d in the general section (p. 20). The uppermost of these divisions, 
b, has a thickness of from 300 to 480 feet, and consists of a series of 
blue, brown, and gray clays with thin beds of limestone. The second 
division, c, has a thickness of 200 feet, and is chiefly blue clay with 
thin-bedded sandstones. The third division, d, comprises blue, red, 
and gray clays and sand carrying Miocene fossils 5 and thin-bedded 
limestones, with a fair proportion of the limestones changed to dolo- 
mite, and is associated with beds of sulphur and coarse sands carrying 
sulphur crystals and beds of pyrites. This division has a thickness 
of 300 feet. It appears to be the chief source of the petroleum and 
gas found on Spindletop and also the source of the petroleum found 
in the other producing fields. The Sour Lake, Saratoga, and Jen- 
nings fields, however, obtain their flow from the associated gray sands 
instead of limestone or dolomite. Division b also carries small quan- 
tities of petroleum and gas, but the blue clays and sandstones appear 
to be barren. 
These beds have been variously assigned to the Cretaceous and 
Tertiary. Professor Harris c places them in .the Cretaceous on account 
« Dumble, Jour. Geol , Vol. II, 1894, p. 544. c Science, new series, Vol. XIII, 1901, p. 666. 
''Determined by Dr. W. H. Dall. 
