244 Review of Recent Geological Literature. 
that of an old base level, about 500 feet high, forming the fiat-topped 
divides of the drainage system, and sliirting the mountains for over 
100 miles west, into Indian Territory, and thence south into Texas: 
It consists of the gravel debris of the Ouachita mountains, is of early 
quaternary age, and has planed ofT and covered the Eocene and Cre- 
taceous strata, and, in turn has been grooved and partially destroyed 
by recent and late quaternary denudation, as recorded in the terraces, 
and deep cut drainage, some 250 feet below the Plateau-Gravel base 
level. The river systems of Arkansas and Texas are described, and 
classified into four sub-groups according to their origin and similarity. 
The Arkansas and Rio Grande rising in the Rocky mountains and cir- 
cumscribing the region are of the first order, the Red, Brazos and 
Colorado of the second, and the Ouachita, Little Missouri, Trinity, 
Nuces, etc. of the third ; while numerous minor streams of post quater- 
nary origin are of the fourth. 
Under the head of "Fundamental Stratigraphy" are defined, discus- 
sed, and named in appropriate local terms six distinct formations 
above the Paleozoic, which is the foundation of the whole group. 
These include over 3500 feet of strata seen, which is a modest esti- 
mate of the whole thickness, and are of lowest Cretaceous, upper Cre- 
taceous, basal Tertiary, early and later, and recent Quaternary ages re- 
spectively. Each of these is described and sub-divided into approxi- 
mate horizons and the exact sequence of every layer shown both 
structurally and chemically (see pp. 220-221), and its relation to the 
Mississippi region in the one hand and the Texas in the other set 
forth ; while upon an appropriate map and sections their exact distri- 
bution is shown. 
Each of these formations is of great interest, and Mr. Hill has suc- 
ceeded in bringing them out clearly. The lowest or Trinity division 
of the basal Cretaceous, is especially interesting, in that it shows the 
exact relation of the base of the Cretaceous to tlie Paleozoic, and adds 
to our geologic section a most important horizon. These beds follow 
the Paleozoic parting west into the Indian Territory and eventually 
crossing into Texas to the south, following the topographic feature 
known as the upper cross-timbers of the latter state. They consist of 
sands and clays, with occasional adventitious layers of shell-breccia, 
(limestone), and contain a molluscan fauna paleontologically almost 
identical with the European Wealdan, associated with huge saurian 
bones and fossil plants which have not been studied. Prof. Hill 
writes that his assistant JNIr. Taff", of the Texas survey, has measured 
over 1000 feet in tliickness of this formation in his region. 
The exposures of the limestone beds of the Comanche Series so great- 
ly developed in the Texas region, stop short at the Arkansas-Choctaw 
line, and are exposed only in Arkansas in the depths of Little river, 
a mile or two from tlie border. 
It is to the development of the upper Cretaceous, and the thorough 
discussion of that formation in Arkansas and Texas and its relation to 
