326 The American Geologist. June, i89o 
of the Cretacic group in this country called Comanche series by 
R. T. Hill has been estimated by us from the different sections 
examined to be 400 feet. 
SECTIONS ON SOUTH CONCHO, 20 MILES SOUTH OF SAN ANGELO. 
1. Hard buff colored limestone, layers several feet thick 30 ft. 
2. Yellow clay with Exogyra texana 30 ft. 
3. White shaly sandstone 40 ft. 
LIST OP FOSSILS. 
1. Gryphiea pitcheri. 5. Trigonia texana. 
2. Exogyra texana 6. Nautilus. 
3. Ammonite f 7. Nerinea texana. 
4. Lima wacoensis. 8. Ostrea f 
The Permian. — This formation in this country conformably 
overlies the Carbonic, dipping from southeast to northwest, 
about 30 feet to the mile and is overlain unconformably by the 
Cretacic deposits. The change from the Carbonic to the Per- 
mian is gradual. The Carbonic forms of life mingling with 
newer types, gradually disappear more and more, giving 
place to the new forms, until in the upper strata of this epoch 
they appear in such abundance, and leading Carbonic forms 
are so rare, that noted explorers have termed it Triassic. The 
clay beds of the Carbonic formations gradually lose their 
black color and appear now variously colored, deep Venetian 
red, blue and yellow, passing frequently through all the differ- 
ent shades. The limestone interstratifying the different Car- 
bonic deposits has changed and has become an argillaceous 
and arenaceous rock of yellowish brown and red color, fr(h 
quently passing into pure sandstone of different colors, white, 
yellow, and sometimes of a deep red. The formation is ex- 
posed above and below the confluence of the Concho rivers, 
and along the Colorado river. Sandstone and limestone de- 
posits of various thicknesses according to sections examined 
from one foot to six feet, are interstratified by clay deposits 
from a few feet to forty or more in thickness. The clay is 
massive or shaly, and the limestone and sandstone are of dif- 
ferent densities, argillaceous and ferruginous. The fossils are 
generally fairly well preserved in an argillaceous limestone of 
drab color, but difficult to obtain on account of the hardness 
of the rocks. Along the Colorado river the gypsum beds ap- 
pear lying conformably upon the older strata of this period, 
forming the highest member of this formation. The Permian 
deposits in this section belong to the southern edge of this for- 
