Vol. V] DUMBLE— TERTIARY DEPOSITS IN NORTHEASTERN MEXICO ^35 



just north of the junction of the Salado and Rio Grande 

 almost to the mouth of the San Juan. On the Rio Grande 

 it carries many fossils connecting it directly with the Clai- 

 borne, together with others distinctively its own, the most 

 prominent of which is the large oyster, Ostrea alabamiensis 

 con tract a Conrad, by which we have identified it as far 

 south as the Conchos. 



The town of Mier is on the Fayette sands, which here 

 have a northeast dip. They are well shown in places along 

 the road from Mier to Camargo and on the river. The up- 

 per beds are a series of yellow sands and greenish yellow 

 cla5's with gypsum, overlying yellow sandy clay with Ostrea 

 contracta, and sandstone beds alternating with yellow clays. 

 Going southwest from Mier we pass over the same beds, 

 until near Borregas at the edge of a scarp facing northwest, 

 we find the lowest Fayette with Ostrea contracta. This is un- 

 derlain at the bottom of the hill by Yegua. About a mile 

 north of Borregas Ranch an outlying hill shows the Fayette 

 as yellowish sand and pinkish sands and clays with leaf im- 

 pressions. The section is : 



Feet. 



Yellow sandstone, Ostrea contracta _. 3 



Yellowish and purple clay 20 



Clayey limestone, fossiliferous 1 



Yellow and pinkish clays... 10 



Yellow sandstone, leaf impressions. 3 



These beds dip N. E. On the Matamoras-Monterey rail- 

 road the Fayette sands begin six miles east of La Laja. The 

 exposures show light gray, almost white, sandstone ranging 

 from two to four feet in thickness, quartzitic in places, and 

 interbedded with softer sands and clays. West of Los Al- 

 damas is a bluff of sandstone with oysters. The top weathers 

 very rough. The Fayette beds have a northeast dip and ex- 

 tend along the railroad some five miles or more east of the 

 river. In the bank of the San Juan River north of China, 

 these sandstones and clays make their appearance and the 

 road from China to Chilarios shows them as a series of 

 gray sandstones and clays, some of the sandstones being con- 

 cretionary and some thin-bedded and ripple marked. Near 



