46 Permo-Carboniferous Ammonoids of the Glass Mountains 



T do not doubt that the determination is exact. This shows that the 

 genus ranges still lower than has been supposed. 



Arthaber has convincingly shown that the fauna of Djulfa belongs 

 to the upper Permian, that it is certainly younger than the Sosio beds, 

 and that it is synchronous with the Kund-Ghat and Jabbi beds of the 

 Upper Productus limestone in the Salt Range of India. 



The preceding review of Permian cephalopod-bearing strata demon- 

 strates that a correlation of the beds is extremely difficult on account 

 of the enormous distance between the different localities, the circum- 

 stance that nearly nowhere a succession of different faunas exists at 

 the same place, and the incomplete descriptions of several of the faunas. 



Notwithstanding these difficulties, I have tried to make the apparent 

 relations between the different faunas more evident by uniting our 

 results in the following comparative tables, following in the second 

 one the method used by Freeh. 



Up to the present time, the question of marine communications be- 

 tween the Trans-Pecos Permo-Carboniferous and the Asiatic and 

 European localities of a similar facies, remains a matter of pure specu- 

 lation. Our data are still extremely incomplete. The Trans-Pecos 

 Permo-Carboniferous is known to exist in a facies that changes rela- 

 tively little in the Guadalupe Mountains, the Glass Mountains, and 

 the Shafter region near the Rio Grande; it is very probable that it 

 continues toward the south into Mexico, and that the locality near Las 

 Delicias northeast of Torreon, Coahuila, is the southernmost place 

 where it has been discovered so far. This locality, which was dis- 

 covered by Haarmann while its fauna was described by Haack, is the 

 only one found in Mexico, so far. In general, the lowest strata of 

 northern Mexico are known to belong to the upper Jurassic or even 

 possibly in some localities in Chihuahua and Sonora, to the Liassic or 

 the Dogger. Marine Triassic has been found by Carl Burckhardt at 

 Zacatecas. where it rests unconformably on older, possibly Paleozoic, 

 schists. It may be possible that older strata than the upper Jurassic 

 could be found some day in the Sierra de Catorce in the state of San 

 Luis Potosi; where according to Joseph Burkart, the rocks of the 

 Jurassic rest unconformably on older shales. Burkart, of course, did 

 not recognize those strata as Jurassic when he described them in 1836, 

 and thought they represented the Carboniferous, but apparently he can- 



