THE C EN O ZOIC DEPOSITS OF TEXAS. 555 



formities exist between the several subdivisions, and even among 

 the beds of the same subdivision. The Carrizo sands show a 

 more or less wavy structure throughout their extent, and this is 

 continued upward into the Marine beds. Some portions of the 

 Marine beds seem to have been subjected to erosion before the 

 deposition of the Yegua clays, and faults of slight throw are 

 quite common. As a whole the beds thicken from the Colorado- 

 Brazos divide to the eastward and toward the Rio Grande and 

 are also more indurated in the latter region. The general dip 

 is south to southeast 10 to 50 feet per mile, although reverse dips 

 are common in places. 



The fossils which these beds hold in common with deposits 

 of similar age of the Pacific slope, some of which are not found 

 in the Tertiary of the Atlantic coast, bear evidence to the fact 

 that the Gulf of Mexico was at that time connected with the 

 waters of the Pacific. The fossils common to these deposits 

 and the Tejon beds are, according to Harris: 1 



Whitney a ^Strepsidura) ficus Gabb, Natica cetitcs Con. equiv. to 

 Nevireta secta Gabb, Solarium alveatum Con. equiv. to Architecto- 

 nica cognata Gabb, Solarium amcenum Con. equiv. to Architected 

 nica hornii Gabb, Cardita hornii Gabb equiv. to Venericardia plani- 

 costa Lam. 



The influx of large amounts of hydrous silica, beds of silice- 

 ous sinter and volcanic ash, and the development of cone-in-cone 

 structure in the upper portion of these deposits is worthy of 

 note as indicating the manner in which these Tertiary deposits 

 became a land area. 



NEOCENE. 



Beds of Neocene age are found both in the Coastal slope 

 and on the Llano Estacado. They probably exist in the trans- 

 Pecos district also, but have not as yet been positively identified. 

 The deposits include beds both of Miocene and Pliocene age, 

 and the following division is proposed : 



'Science, August 16th, 1893. 



