[PENHALLOW] NOTES ON FOSSIL WOODS FROM TEXAS 101 
west, where it sometimes happens that considerable hills occur, the 
summits being capped by the harder sandstone of the Fayette beds.’ 
He describes the clays as “dark blue, weathering to dirty yellow with 
a profusion of crystals of gypsum. In places the clays are massive, 
at others laminated. The fossil wood contained in them is simply 
silicified, not opalized as in the succeeding beds’ And finally, he 
notes that there is no sharp line of demarcation between the Yegua 
clays and the Fayette sands which overlie them. 
Kennedy deals with the Yegua clays somewhat more at length, and 
points out that the Trinity River section shows the typical Yegua clays 
in many of its bluffs (8, 104), although the Yegua River, forming 
the southern boundary of Burleson County, is the one which gives name 
to the formation (op. cit. 99). “Throughout east Texas these beds 
contain numerous plant remains in the form of silicified and lignitized 
wood, and leaves of many kinds are extremely abundant. None of 
these have as yet been studied, but from the fact that silicified palm 
wood occurs, although sparingly, in the upper gray sands, the climate 
was slightly warmer than at present.” 
“The general conditions of deposition during this period appear 
to have been those of a marsh subject to periodical deep, widespread 
inundation and a gradual though slow subsidence. The marine beds 
lying to the north, evidently stood at a much higher relative level than 
at present.” (pp. 105-106). . 
In discussing the geology of the eastern area of Texas, the same 
author (op. cit. 93) states that “Into the general section, however, 
three divisions of the Lisbon Stage have to be introduced, all of which, 
so far as at present known, are peculiar to Texas. These are (a) Frio 
clays, (b) Fayette sands, and (c) Yegua clays. These overlie the 
marine beds in the reverse order here given, and together aggregate 
a thickness of nearly 1,500 feet in east Texas, while farther west this 
may be considerably exceeded.” 
In discussing the possible correlation of the Texas Eocene with 
the Mississippi section of Hilgard, Kennedy also observes (op. cit. 107), 
that “ The correlation of the Frio clays, Fayette sands and Yegua clays 
with the deposits of Louisiana lying immediately to the east, is attended 
with more or less difficulty and doubt from the fact that little or no 
work, and that of the most general character, appears to have been 
done in that portion of the state. The Grand Gulf, according to 
both Hilgard and Hopkins, appears to have embraced the two upper 
and at least a portion of the Yegua clays, besides the upper calcareous 
sandstones, and was, according to these writers, above the Vicksburg. 
The lower portion of the Yegua clays was apparently considered by 
