134 CALIFORNIA ACADEMY OF SCIENCES [Paoc. 4th Sek. 



are nummuHtes and orbitoides, with a few undetermined mol- 

 lusks. 



In the northern portion of the area, west of the Tamaulipas 

 Range, no beds were found which, because of their fossils, could 

 be positively referred to the Tertiary. However, certain sandy 

 shales were seen along the railroad north of the Panuco River, 

 and on the San Antonio River west of Cruz there are hills com- 

 posed of shales which lie nearly horizontally, while the under- 

 lying shales have a strong dip northwest. These shales closely 

 resemble the Chicontepec in composition, and Cummins con- 

 siders them of that age. 



Near Padillo, which is at the junction of the Purificacion 

 and Pilon rivers, east of Victoria, similar sandy shales were 

 observed, and these may possibly be Chicontepec also. It is not 

 thought probable that any of the shales west of El Abra Moun- 

 tains are later than Papagallos, but, from Las Palmas eastward 

 to Mendez, part or all of the shales are probably Chicontepec, 

 and this condition continues southward. 



Chicontepec 



The Chicontepec beds are best seen in the extreme western 

 portion of the Embayment area south of Aquismon, and 

 especially in the hills lying just east of the great Cretaceous 

 escarpment. 



In places they are strongly folded as in the Chicontepec 

 Mountain and almost everywhere show much stronger dips 

 than the overlying Oligocene. 



The Chicontepec beds proper seem to have been folded and 

 eroded prior to the deposition of the Alazan shales. 



From a locality in the Aquismon district, some 25 miles south 

 of Valles, Jeffreys describes the following deposits, which he 

 names the Tanlajas formation. 



The Tanlajas series, as a whole, averages probably about 

 1100 feet in thickness. It consists, in the main, of marine de- 

 posits of rapidly alternating sandy limestones and shales. The 

 base is composed of 250 feet of alternating beds of thin, sandy 

 limestones, calcareous sandstones, and gray shales. The upper 

 portion of these beds has one or two beds of calcareous blue 

 sandstone, weathering to dark brown, which average, in places, 



