R. T. Hill — Cretaceous Formations of Mexico. 313 



Sonora from a collection of fossils made by Remond. The; 

 fossils are the characteristic fauna of the latest or Washita 

 division of the Comanche Series and resemble the variations 

 seen at El Paso and Juarez and throughout the northern lit- 

 toral of the latest beds of the Comanche Series and belong 

 neither in the Upper Cretaceous formation nor below the 

 Caprina (Hippurites) limestone, as Prof. Heilprin indicates in 

 the paper previously mentioned. 



From these data it is evident that the three prominent 

 stratigraphic divisions of the Comanche Series are recognizable 

 in Mexico as in Texas and when the whole region is studied 

 more detailed resemblances of horizons will be discovered. 



Age and Homotaxial relations of the Comanche Series in 

 Mexico and Texas. — The diverse opinions concerning the age 

 of the Mexican Cretaceous have been indicated. Felix and 

 Lenk maintain the Neocomian age of the Tehuacan beds and 

 have little to say concerning the so-called " Hippurites " lime- 

 stone. Most of the Mexican geologists speak of the Hip- 

 purites limestone as probably Upper Cretaceous. Prof. Heil- 

 prin emphatically maintains the Upper Cretaceous age not only 

 of the Mexican but of all the Texas Cretaceous. This conclu- 

 sion is based upon the same evidence that caused Dr. Rcemer 

 to make the same mistake in Texas, to wit : the occurrence 

 of the alleged "Hippurites" and Nerineas in the limestone, 

 and Prof. Heilprin's mistaken idea that the writer of this 

 paper holds that the faunas of the Fredericksburg and Washita 

 divisions of the Texas section represent the Neocomian in- 

 stead of the Glen Rose and Trinity beds, with the faunas of 

 which he (Prof. Heilprin) is evidently unfamiliar inasmuch as 

 they have not been fully published. The writer has endeav- 

 ored to reserve his views on the homotaxial relations of the 

 North American Cretaceous for a future and exhaustive publi- 

 cation and can say but little concerning them now. In the 

 first place the genus ISTerinea which Prof. Heilprin and others 

 consider a characteristic genus of the European Senonian, 

 ranges in Europe from early Jurassic time to the top of the 

 Cretaceous, while in America it extends no higher than the 

 Caprina limestone of the Fredericksburg division of the Lower 

 Cretaceous, not a single species appearing in the great Upper 

 Cretaceous or Meek and Hayden section of the United States. 

 Furthermore this genus has many sub-generic features each 

 with its peculiar stratigraphic range and all the species de- 

 scribed from Texas by Rcemer and Conrad and from Mexico 

 by various writers are of the characteristic early Cretaceous 

 type. The occurrence of the alleged " Hippurites," however, 

 prevented Rcemer, Heilprin and others from understanding 

 the true position of these beds, notwithstanding the testimony 



