600 TIMOTHY WILLIAM STANTON 
San Antonio to the Rio Grande at Del Rio, covering large areas 
west of that line. It is known to underlie a large part of 
Mexico, extending as far west as Arivechi in Sonora. Small 
outlying areas occur in southern Arizona, at El] Paso, Texas, 
in eastern New Mexico, in Oklahoma, and in southern Kansas. 
The stratigraphic details have been published mainly by Messrs. 
Ry Ue Bi fs AN enae, 185 1, IDimanole, We Je. Conamamins, 10, \\) . 
Vaughan, and C. S. Prosser. 
The main features of Mr. Hill’s classification of the deposits 
are as follows: 
( Shoal Creek limestone, 
’ Washita | Denison beds, 
1 Fort Worth limestone, 
| Preston beds. 
| Caprina (Edwards) limestone, 
Comanche series ~ Fredericksburg + Comanche Peak limestone, 
| Walnut clays. 
io Paluxy sands, 
| Trinity Glen Rose limestone and clays, 
: | Trinity sands. 
This list gives the principal recognized subdivisions and ind1- 
cates the lithologic character of the section in central Texas. 
Calcareous sediments of varying texture and composition largely 
predominate over all other kinds, thus contrasting strongly with 
the Shasta deposits. Considerable beds of sand are locally 
developed in the lower or Trinity division, and in the middle of 
the Washita clays and sandy layers usually predominate, but as 
a rule much more than) halt of the total thickness or sthe 
Comanche series consists of calcareous beds. Near the borders 
of the Comanche sea the limestones decrease in relative thick- 
ness or disappear entirely. At El Paso they form but a small 
proportion of the section, and in the Tucumcari region of New 
Mexico and in southern Kansas the rocks are all sandstones and 
clay shales. In the latter region the total thickness is only 
about 200 feet, and apparently the Washita division is the only 
one represented. In central Texas the entire series has a thick- 
ness of about 1500 feet, which increases southwestward, until 
