Geologic Story of the Colorado River. — Hill. 289 
1. Quaternary. Thickness. 
1. Older Terrace deposits of Colorado river at Austin, superficial. 
1 a. Upland gravel as seen at McDade, superficial. 
2. Tertiary. 
Eo-Lignitic ("Laramie") or basal Eocene, Bastrop 
county i:)robably 1 )000 
3. Upper Cretaceous. 
a. Upper arenaceous beds, eastern edge Travis 
county 300 
b. Middle (Exogyra ponderosa) marls, east half of 
Travis county 1.000 
c. Austin or Niobrara chalk, city of Austin 600 
d. Eagle Ford or Benton shales, city of Austin 300 
The Loioer Croas- Timber or Dakota sands are missing 
here; present in North Texas 200 
4. Lower Cretaceous. 
a. Vola limestone, or Shoal Creek horizon, Austin 50 
b. Exogyra arietina clays, west of Austin 100 
c. Washita limestone (metamorphosed chalk) west 
of Austin 160 
d. Medial or Hippurites limestone (metamorphosed 
chalk) AVest of Austin 900 
e. Basal or Fredrickburg limestone, (metamorphosed 
chalk) Burnet 300 
f. Trinity, basal littoral beds, Burnet 300 
5. Carboniferous. 
a. Bituminous shales and sandstones. Marble Falls 
and Smithwick 300 
b. Encrinital, or Marble Falls limestone 500 
('>. Silurian 
Barren white limestone l)eds, Lower Marble Falls. 
7. Cambrian. 
i Indeterminate limestone flags 1,150 
a. Upper - Potsdam sandstones; western Burnet 
/ tounty 625 
b. Lower.— The Llano group of Walcott, Sand mountain. .2,000 
Total 9,520 
It is impossible to give the details of each of these forma- 
tions. The general character of the paleozoic section has 
been defined b}^ Walcott,* except the Carboniferous. The 
writer has previonsl}' defined the Cretaceous with the excep- 
tion of the horizon here mentioned as the Vola limestone, 
which is new. The basal Tertiary or Eo-lignitic beds have 
been studied by the writer and others during the past year 
from the Rio Grande to the Alabama. The Quaternary beds 
will be more fully defined later. 
UNCONFORMITIES AND DISTURBANCE. 
This section presents an extensive perspective of the strati- 
graphic history of the region from earliest Cambrian to the 
present. As previously shown by Walcott, the Llano beds are 
* Notes on tht- Paleozoic rooks of Central Texas. Am. Jour., Sci. Dec, 1S84. 
