Review of Recent Geological Literature. 385 
but have prevailingly a slight dip to the southeast, toward the Gulf 
coast, somewhat exceeding the average surface slope, which declines 
from about 1,500 feet at the west to 400 feet at the east above the sea 
level. 
From paleontologic studies of this development of the Cretaceous 
system in Texas, Mr. Hill finds it "divisible into two great groups or 
series, each of which ia turn is composed of many beds of rock. The 
lower of these series begins with the Trinity sands and ends with the 
Denison beds, and has been named the Comanche series, after the town 
of Comanche, where the writer, when a. boy, first studied these form- 
ations. The upper series begins with the Woodbine formation and ex- 
tends through the Navarro beds ; this has been termed the Gulf ser- 
ies. Each of the series represents a complete cycle of sedimentation 
and is initiated by an arenaceous littoral terrane." 
A running summary of the fifteen formations making these Lower 
and Upper Cretaceous series, aggregating together about 4,500 feet in 
thickness, is given as follows: "The lowest Cretaceous formation (i) 
resting on the Paleozoic rocks and outcropping at the surface in the 
belt' of Western Cross Timbers consists of loose beds of friable sand 
(locally called pack sand), with a few pebbles at its base (the Trinity 
sands). These sands pass upward into (2) light-colored arenaceous 
clays and marls in which alternating layers or beds of firm limestone 
of varying texture and thickness gradually appear. The marls and 
limestones are the Glen RoSe beds. Another thick bed (3) of pack 
sand (the Paluxy sands) succeeds the Glen Rose beds. The outcrop 
of the Paluxy sands is covered with timber. Above the Paluxy sands 
are (4) claj'S alternating with thin limestones, usually accompanied 
by vast numbers of fossil oysters. These, the Walmut beds, pass up- 
ward into (s) white chalky limestones (the Comanche Peak beds), 
which are very fossiliferous and which usually constitute lower slopes 
of the escarpment of flat-topped mesas or plains. The Comanche Peak 
beds are distinguishable from the succeeding bed (6) of white chalky 
limestone (the Edwards limestone) only by the superior hardness of 
the latter, which is the rock of the numerous flat-topped buttes of the 
western border of the Grand Prairie and in which, at least south of 
the Brazos, are numerous beds of flint. The limestone, which is not 
very thick along the section under consideration, is succeeded to the 
east by another group of beds making the surface formations of the 
dip plains of the Grand Prairie between the western scarp rock and 
the Eastern Cross Timbers and consisting of alternations of marls and 
indurated layers of limestone. The lowest beds of this group consist 
of (7) darker-colored clays (the Kiamitia clays) containing great 
quantities of another fossil oyster. Above these appear more bands 
of limestone strata (8) of a chalky white color, alternating with clays 
(the Duck Creek formation) in which huge ammonites a foot or more 
in diameter are found. Near the top of these alternations of marls is 
a group (9) of whitish limestone beds (the Fort Worth limestone) 
in which limestones and marls alternate with great regularity. Fort 
