138 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Sea. 



At El Xuchil the blue and brown clays and shales are inter- 

 bedded with brown sandstones, carry clay ironstone nodules in 

 places, and gradually pass downward into sandstone. 



At Sabanita the upper beds are gray to green shales, marls 

 and clays with shaly sandstones and limestones grading down- 

 ward into impure thin-bedded limestones interbedded with 

 similar shales and with beds of tuff of variegated colors. 



The materials of De Golyer's San Felipe, however, are ap- 

 parently unconformable on the Tamasopa, and are very differ- 

 ent from those found in the San Juan farther north, and if, as 

 he suggests, such fossils as it contains are of Eocene age, his 

 San Felipe can not possibly be correlated with the San Juan, 

 which is undoubtedly Cretaceous. Furthermore, his overlying 

 Mendez differs materially from that north of the Panuco River, 

 and agrees more nearly with the upper portion of the Chicon- 

 tepec beds of which we believe it to be the southern extension. 



Similar shales appear in many of the exposures examined 

 between the Panuco and Tuxpam rivers. 



On the Tlacalula Ranch, northeast of El Xuchil, there are 

 many exposures of beds similar to those between Chicontepec 

 and El Xuchil. In many places the shales are standing at high 

 angles and are cut by basalt dikes and frequently are impreg- 

 nated with asphalt. They are blue to gray in color, interbedded 

 with brown sandstones, and occasionally have bands of clay 

 ironstone. 



These are found in the beds of such creeks as Puente, Palma, 

 and Coyote, and near the river Tamozus. 



They are also found in the base of Mount Santo Domingo 

 and between it and Cerro Tultepec. To the eastward they are 

 found around Horcones and on the Buena Vista River at Ala- 

 zan. Jeffreys reports them as underlying his Oligocene section 

 at Temapache, six miles southeast of Alazan. 



Southeast of Tamiahua, on the San Marcos River, Sands 

 found good exposures of them and furnishes the following de- 

 scription : 



"The beds are composed of bands of very hard light blue- 

 gray, fine-grained calcareous shale which in places becomes 

 almost a shaly limestone and varying in thickness from two 

 inches to a foot, interbedded with softer bands of thicknesses 

 varying from a few inches to fifteen feet. Some of these softer 



