Vol. V] DUMBLE— TERTIARY DEPOSITS IN NORTHEASTERN MEXICO Jg^ 



Another quarry to the south of this, on the ridge dividing 

 the river and Ayancual Creek, shows the same hmestone 

 with the same fossils and they are seen again at the head of 

 an old irrigation ditch near Hacienda Nueva, five miles west 

 of Herreras. North of the river the Midway includes a series 

 of interstratified blue and brown, shaly clay and gray, brown 

 or white sandstones which extend for several miles and find 

 in the Alto Colorado their most conspicuous development. 

 This hill is three miles north of kilometer 1121 on the 

 railroad. It shows the following section : 



Feet. 



Brownish gray, heavy bedded sandstone 3 



Limestone, fossiliferous 1 



Brownish sandstone 8 



Blue clay, weathering yellow. ^ 



Yellow brown sandstone, somewhat calcareous, 



fossiliferous — 160 



Yellow, shaly clay 80 



The fossils are not very well preserved, but include Ostrea 

 pulaskensis, O. crenulimarginata, Vcnericardia planicosta, V. 

 alticostata, Turritella, and other undetermined gasteropods. 

 The same beds were also observed 16 miles southeast of Ra- 

 mones on the road to China, which was the most southerly 

 exposure of them which we could identify. 



A mile southeast of Comitas, on the road from Ramones 

 to China, there is an exposure of typical Wilcox strata but 

 without any fossils. It consists of heavy beds of clay with 

 nodules of clay ironstone, weathering red. 



Claiborne 



Carrizo 



South of the Pesqueria, sandstones, probably referable to 

 Carrizo, were seen 2^ miles west of San Juan and there 

 was also seen a gray sandstone with westerly dip a few 

 miles north of Vaqueria, which may represent it. The great- 

 est development of these sands, however, both in Texas and 

 Mexico, is found in the drainage area of the Rio Grande. 



