J75 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Between Soto la Marina and San Rafael the only contacts 

 observed were between the San Fernando and the eruptives 

 lying east of the Tamaulipas Range. 



THE TERTIARIES 



Our examination of the deposits occurring along the Rio 

 Grande and overlying the Escondido failed to show any 

 beds of the Eocene of later age than the Frio substage of 

 the Claiborne. This was followed directly by our Oakville 

 or upper Miocene. No Oligocene or lower Miocene are pres- 

 ent there, so far as our present knowledge serves. 



The formations recognized are -^ "^- ^- ''■ ^ 



Frio 

 Favette 



Claiborne 



Yegua 



Marine 

 Carrizo 

 Wilcox, 



Midway. 



Between the Rio Grande and the Conchos, however, we 

 find the Oligocene coming in between the Frio and overlying 

 materials and to the south it attains a strong development. 



Briefly stated, the characteristics of the several divisions of 

 the Eocene as known on the Rio Grande are as follows : 



Midway 



Gray clays with limestone concretions overlain by bluish 

 shales and shaly sandstone interstratified with ferruginous 

 sandstone, both series carrying V enericardia alticostata, V. 

 planicosta, Ostrea pulaskensis, Cucullcea macrodonta and 

 other forms, 



Wilcox 



A lower series consisting of blue and gray sandy shales, 

 light gray sandstones and bluish, carbonaceous, sandy shale 



5 Dumble, E. T., "The Cenozoic Deposits of Texas," Jour. Geology. 



6 Vaughan, T. W., Reconnaissance of the Rio Grande Coal Fields of Texas, U. S. 

 G. S., Bull. 164, 1900. 



7 Dumble, E. T., "Geology of Southwestern Texas," Trans. Am. Inst. Min. Eng., 

 1902. 



8 Dumble, E. T., The Carrizo Sands, Trans. Tex. Acad. Sci., 1911. 



