Vol. VIII] DUMBLE— GEOLOGY TAMPICO EMBAYMENT AREA 127 



the floor of the valley for 25 miles southeast of Linares to 

 the foothills of the San Carlos Mountains, in the elevation 

 of which the San Juan is again brought up. 



The San Carlos and Cruillas mountains, lying between the 

 Conchos and Sota la Marina rivers, are composed of heavy- 

 bedded, compact limestones (Tamasopa ?) overlain by thin- 

 ner bedded fossiliferous limestones of the San Juan series 

 followed by the Papagallos shale. On the northern or Con- 

 chos River face of the mountains the Cretaceous is overlain 

 by the sandstones and clays of the Fayette substage of the 

 Eocene which are last seen on the Choreras arroyo east of 

 Cruillas; the Fayette is overlain in places by the San Rafael. 

 On the southern face of the mountains the Sota la Marina 

 drainage, on the contrary, shows the yellow sandy clays of 

 the San Rafael directly overlying the Papagallos or earlier 

 members of the Cretaceous. 



Between Linares and Cruz the Papagallos shales were found 

 exposed at Summit, Carrizo, and other points, and simillar ex- 

 posures are found in the valley for 25 miles eastward. At 

 Cruz they are exposed in the bed of Purificacion River and in 

 the same river northwestward to Hidalgo, just west of which 

 are hills composed of the San Juan limestone. The valley 

 between these hills and the Sierra Madres shows the upturned 

 edges of the shales which are finally cut out by the scarp 

 of Tamasopa limestone. Between Cruz and Victoria the sur- 

 face is largely covered with drift or Reynosa, but these sur- 

 face deposits are cut through in many places and the under- 

 lying hardened blue shales can be seen dipping at a strong angle 

 to the west. These shales were also seen just south of Victoria 

 and in numerous gulches between Victoria and San Francisco. 

 At San Francisco there is a well 90 feet deep in these shales 

 and they are exposed at many different places between San 

 Francisco and Gonzales where a well 1,500 feet deep was 

 in the shale its entire depth. To the east of the railroad 

 similar shales were found at Los Esteros and Mendez. 



From this it will be seen that the valley between the Sierra 

 Madre on the west and the TamauHpas INIountains on the 

 east from San Juan to Gonzales and Los Esteros is under- 

 lain throughout by a body of blue shales. 



At Mendez a well was drilled which passed through a 

 thousand feet of shale before entering the platy limestone of 



