Vol. V] DUMBLE— TERTIARY DEPOSITS IN NORTHEASTERN MEXICO 175 



in them, here and there, massive bhie nodules or boulders 

 which weather white. To the east of these hills lies a valley- 

 two miles wide, and the hills which form its eastern margin 

 are composed of the sands and clays of the Midway. 



The Papagallos Mountains lying west of Ramones rise 

 somewhat abruptly from the river and at the distance of a 

 mile attain an elevation of 800 feet. So far as can be seen, 

 the range is made up of highly metamorphosed blue shales, 

 which weather white on exposure and which have been folded 

 into a sharp anticlinal, the dip of which on its eastern slope 

 is as much as 60 degrees, while the dips on the west vary 

 from 30 to 70. The entire valley to the west seems under- 

 lain by the same shales but with greatly lessened dips, and 

 these form small hills at Ayancual and elsewhere. These 

 shales also stretch to the east and exposures on the river 

 show that they were considerably disturbed and crumpled 

 prior to the deposition of the Eocene beds. These beds were 

 not traced between the Pesqueria and the Conchos, the line 

 of travel lying east of them and over the Tertiary deposits. 



On the Conchos River the conditions appear to be similar 

 to those on the Salinas and the only exposures of the Papa- 

 gallos shales seen were in the river below the Tertiary beds. 

 The main body of the Cretaceous deposits lies west of 

 Vaqueria. They then swing eastward around Burgos Peak, 

 southeast of which the San Juan limestone is found in a 

 canyon. From this locality several poor specimens of am- 

 monites, including a Mortoniceras (?), sp. were collected, of 

 which Dr. T. W. Stanton says : "The genus Mortoniceras 

 occurs in the San Carlos beds, in the Austin chalk, and in 

 the Tombigbee sand. If correctly identified, the presence of 

 this genus probably means the limestone is not younger than 

 the Taylor marl and may not be younger than the Austin 

 chalk." To the southeast of this on the road to Cruillas the 

 blue shales come in again. Northwest of Abasolo the San 

 Juan limestones appear, while Abasolo itself is on the blue 

 Papagallos shales and these extend southward along the 

 river as far as Soto la Marina, at which place they are also 

 found in wells. In this region they are overlain in places 

 by the yellow clays of the San Fernando and by the Coquina 

 limestone and the Reynosa. 



