Geologic Story of the Colorado River. — Hill . 297 
upper Cretaceous sands and marls. With the exception of the 
beginning of the great Atlantic timber belt there is no sharply 
defined topographic line of demarcation between them. After the 
first hundred feet there are great beds of lignite derived from 
the post-Cretaceous continent. They continue northward to 
Alabama and south to the Rio Grande. 
THE QUATERNARY. 
Reaching half way across the Lignitic and uppermost Creta¬ 
ceous areas, are great beds of gravel composed of quartzites 
entirely foreign to Texas and smilar to those of the Hatcha- 
tigbee gravel of Alabama and the drift of south-western 
Arkansas and connected with them by probable continuity. 
This is probably an accompanying phenomenon of the 
great glacial depressions at the north. 
ANCIENT RIVER TERRACES. 
• From an altitude of 150 feet above the Colorado at Austin to 
within 50 feet of its present level there is a series of ancient ter¬ 
races composed of quartz and flint, accompanied in the young¬ 
er terraces by red clays which have been removed by lixiviation 
in the older benches. This gravel quartz and flint is the 
remnant of the granite and chalk of the Burnet and lower 
Cretaceous region, the feldspar and chalk having long since 
decomposed. In the terraces we have the record of three im¬ 
portant events, to-wit: The change of level of the land in 
late Quaternary time; the amount of degradation the Burnet 
granite has undergone, which can be also shown by studies 
of the granite area proper, and finally an idea of the immense 
amount of the chalk removed as recorded by the flints. These 
terraces do not extend westward of the scarp at Austin, but 
are well marked to the east. 
DISTURBANCES IN THE CRETACEOUS FORMATIONS. 
Throughout the two Cretaceous formations and possibly 
the Tertiary there are numerous disturbances which throw 
much light upon the history of the region. These disturb¬ 
ances belong to two classes, the first of which occurred during 
or at the close of the early Cretaceous and the other at the 
close or later than the later Cretaceous. 
The first class of the disturbances is shown in the excessive 
dip, faulting, and folding of the strata in a manner different 
from anything found in the later Cretaceous. The structure 
