312 It. T. Ilill — Cretaceous Formations of Mexico. 



arrangement and littoral characters the Trinity beds of the 

 Comanche Series in Texas, but contain one genus, Rhyncho- 

 nella, and many different species including several described by 

 Felix and Lenk from southwest of Tlaxioco including Iloplites 

 tenochii, H. neocomensis D'Orb., Tylostoma princeps White, 

 and a large Terebratula very much resembling the form figured 

 as Inoceramus montezumi by Felix. 



Similar basement beds of the mountain limestone are re- 

 ported at Catorce and near San Luis Potosi. From the latter 

 locality Nikitin has noted* a fauna resembling that of Mique- 

 huana, but also containing the California and Russian species 

 of Aucella and refers the beds to the upper Jurassic. Near 

 Bustamente these basement beds are metamorphosed into schists 

 owing to the intense folds of the mountain as seen by JVIcGee 

 and the writer. 



Felix presents strong arguments for the Cretaceous age of 

 the basement beds, notwithstanding the somewhat Jurassic 

 facies. The basement Trinity beds of the Texas region are 

 clearly the Wealden i3hase of the Neocomian and these Mique- 

 huana beds are this southward continuation and confirm the 

 fact that the great littoral of the subsiding land in earliest 

 Cretaceous time advanced from the south northward. 



The " Hippurites" limestone is not the top of the Lower Cre- 

 taceous formation in Mexico, much less the top of the Upper 

 Cretaceous or the equivalent to the Upper Cretaceous of the 

 United States as supj)osed by Drs. Felix and Lenk, for in 

 northern Mexico at various places I have found it overlaid by 

 the beds of the Washita division of the Comanche Series and 

 this in turn overlaid by the Upper Cretaceous of Meek and 

 Hayden. Near Monclova and Santa Rosa in Coahuila the 

 Washita beds aj)pear as thinner limestone flags and shales 

 overlying the lower limestones and contain the characteristic 

 gryphseas and ammonitidse of the division. The beds of this 

 division cross into Mexico at several places along the Rio 

 Grande. Opposite Del Rio Texas the Exogyra arietina zone 

 of the Denison beds of the Washita division extends far into 

 Mexico. West of El Paso at the international boundary the 

 beds of the Washita limestone division occur on both sides of 

 the river, the famous pass of the Rio Grande at that point 

 being in rocks of the Fredericksburg and Washita division. 

 The Washita beds here include both the Fort Worth and 

 Denison subdivisions and are largely developed in the moun- 

 tains of northern Chihuahua. Gabbf in 1863, before the 

 stratigraphic identity of the Comanche Series had been made 

 known, recognized the extension of the Texas Cretaceous into 



* Jahrbuch fur Mineralogie. 1890, ii, pp. 273-274. 



f Geological Survey of California, vol. ii, Sec. Ill, p. 255. 



