3003 =6R. 7. Mill—Cross Timbers in Northern Texas. 
Immediately underlying this Rotten limestone, and chiefly 
exposed beneath its projecting stratum, along the escarpment 
base, are several hundred feet of barren argillaceous shales (c), 
yellow above, and gradating into blue black at the base, with 
the huge septaria so familiar to one who has seen the Niobrara 
shales of the west. Where the protecting limestone has been 
washed away, the shales weather into a gently undulating 
prairie, with a predisposition to that character locally known 
as “hog wallow.” This is the second character of prairie, a 
prairie resulting from weathering of shales; it extends as 
a narrow strip along the western edge of the Rotten limestone 
region, but fades out before reaching the center of the State. 
Continuing westward the next topographic feature is the 
belt of forest region known as the ‘Lower Cross Timbers.” 
Geologically the area occupied by. these timbers consists of a 
series of coarse, friable, arenaceous sandstones, (d) alternating 
with clays, whose position is beneath the shales and limestones ; 
and, like them, its western projecting margin is constantly 
wearing away. The unique fauna, now being studied by Dr. 
C. A. White, and the presence of lignites, indicate that the 
sediments are those of shallow waters; they resemble the 
basal groups of the cis-Mississippi region,* and, Dr. White be- 
lieves, the Dakota sandstones of Kansas. Elsewhere than in 
Texas this group would be considered the base of the Creta- 
ceous; but such is not the case here, for it clearly rests upon four 
hundred feet of a second, and lower series of limestone strata (e) 
and one that was greatly eroded before these sands were 
deposited. This is the “Texas” group of the American 
Cretaceous—the-probability of the existence of which I pointed 
out in a previous paper, and which is now demonstrated to be 
lower than any of the hitherto described marine Cretaceous of 
this country. 
This limestone formation underlies the third character of prai- 
rie, which extends parallel with and between the two Cross Tim- 
bers. The strata are bands of varying thickness of yellow-white 
limestones of a peculiar structure, alternating with calcareous 
clays and marls of the same color. The prairie extends from 
four miles east of Fort Worth to seven miles west of Weather- 
ford. In crossing it the strata from top to bottom are succes- 
sively passed. Its surface is barren and rocky, excepting in 
rainy seasons, and slopes at a much greater angle to the 
southeast than the others we have described. This was known 
to old travelers as the ‘‘Grand Prairie,” a term which is worthy 
of preservation. One of the strata of limestone (e’) presents a 
* This and all strata above it in Texas are a continuation of the Alabama, 
Tennessee, Mississippi and Arkansas Cretaceous and Tertiaries, to which I give 
the name of Gulf series. 
