324 The American Oeologist. luue, i89o 
buffalo and antelope ; and the cultivation of the soil, roads 
and railroads and works of irrigation are changing daily its 
surface features. 
Recent Geolog-y. 
Alluvium. — The river bottoms or valley lands, formed in re- 
cent periods through rains and wind, frost and sunshine, with 
the powerful aid of carbonic acid contained in the atmosphere, 
are derived from the underlying Cretacic and Permian strata. 
These are in thickness from 20 to 30 feet, in some places inter- 
stratified with loose gravelly deposits. The uplands are cover- 
ed with alluvial soils generally from two to five feet thick. 
Drift. — Beds of hard limestone conglomerate situated along 
the rivers and creeks are often 50 to 60 feet thick. They are 
purely local, as is evinced by the large size of the boulders, 
and from the fact that they are of limestone from the sur- 
rounding strata. Frequently the boulders are but little water- 
worn, evidently having been rolled but a short distance. We 
have been unable to determine with certainty the age of these 
deposits, as no fossils have been found in situ. Yet it is most 
probable that an inland sea covered the Staked Plains, till in 
diluvial times an elevation of the western side of the conti- 
nent took place, and the waters of this vast sea commenced 
flowing toward the gulf, leaving the valleys and these beds as 
evidence of their action. 
Lacustrine Deposits. — Succeeding the drift epoch are depos- 
its of an ash-gray or brownish color containing sand and clay, 
and generally spotted with small white calcareous concretions. 
They have been dejDosited by quiet waters in basins forming 
lakes and lagoons. They are sometimes found 30 feet thick, 
generally overlying or leaning on the drift. No fossils have as 
yet been found in the loess of this country. The deposits of 
this material have been made in basins of comparatively small 
size along the river channels, their size depending on the gen- 
eral width of the valley. The rivers in cutting their way 
through them have left these deposits exposed in steep bluffs 
and eml)ankments. The composition is a calcareous sandy 
loam of a light yellowish lirown color, very porous, with a 
number of calcareous incrustations. The material is unstrat- 
ified. 
The Cretacic — Preceding the drift, covers the larger part of 
the Concho country. It rests unc()nformal)ly on the Permian, 
