106 GEOLOGY AND PALEONTOLOGY. 



OBSERVATIONS UPON THE CHAEACTEE AND GEOLOGICAL AGE OF THE 

 SPECIMENS OF ROCKS AND MINERALS SUBMITTED TO MY EXAMINATION 

 FROM THE COLLECTIONS OF THE UNITED STATES AND MEXICAN BOUN- 

 DARY SURVEY. 



I. Specimens from t]ie Gulf Coast, Texas, as far as El Paso, including all those from the east side 



of the Bio Grande. 



1. Calcareous sandstone, branch of the Guadaloupe river below San Antonio. This rock is 

 apparently of Tertiary age, and presents nothing peculiar in its character, except its loose 

 aggregation and numerous dark siliceous specks or grains. 



2. Calcareous conglomerate, fifteen feet thick. 



These specimens bear the character of the Tertiary sandstones known in Kansas and 

 Nebraska. They are sometimes highly calcareous. The sandstone varies in character from 

 loosely aggregated and incoherent sand to a compact calcareous sandstone or quartz rock, for the 

 grains sometimes appear to have been cemented by fluid silica. 



From information obtained in connexion with these specimens, the strata to which they 

 pertain occur in outliers of greater or less extent, the original formation having been subjected 

 to extensive denudation. The similarity in lithological character and association suggests a 

 probable identity in age between these beds and those of the Mauvaises Terres of Nebraska; and 

 that the Tertiary is probably co-extensive with the cretaceous formation from Nebraska to Texas 

 and New Mexico. 



3 and 4. Argillaceous, buff-colored limestone, a thickness of fifty feet, ascertained in sinking 

 a well, while the entire thickness of the rock is much greater. This rock is used for buildings 

 in San Antonio. It has the same lithological character as the stratum which elsewhere contains 

 Inoceramus mytiloides. — I. prohlematicus. 



5. A yellow granular limestone of similar character, but more compact than the limestone of 

 Timber creek. New Jersey. The specimen contains a species of cardium. The rock from which 

 this specimen was obtained occurs about twenty miles further to the west than Nos. 3 and 4, 

 and is penetrated in reaching a more compact stratum below. 



These specimens are from the lower part of the cretaceous formation. 



a. Specimens from the table-land on Devil's river. 



6. Light gray limestone with cretaceous fossils. Painted caves. 



'7. A more granular limestone than the preceding, resembling No. 5 in character, and con- 

 taining valves of an Ostrea. Painted caves. 



8. Compact, reddish brown granular limestone, containing Nodosaria. This rock, on its 

 weathered surface, is of the character of the preceding, but more compact and crystalline in its 

 texture. 



9. Compact, subcrystalline, yellowish limestone ; sometimes of a brownish yellow. Table- 

 land beyond Devil's river. 



10. Vesicular trap from isolated hills and ridges rising from the table-land. 



