24 University of Texas Bulletin 



be certain and this would correlate the Delaware Mountain beds with 

 our Word formation (zone of Waagenoceras). This is confirmed by 

 the existence of a form described as Gastrioceras sp., which has 

 most intimate relations with our Gastrioceras n. sp. indet. With the 

 exception of the Gastrioceras serratum Girty, the rest of the ammo- 

 noids have been found in higher strata ; nothing similar to them seems 

 to occur in any of our beds. The brachiopod fauna of the Word forma- 

 tion contains a number of species also found in the Delaware Mountain 

 beds and therewith confirms our supposition that both are contempor- 

 aneous ; but we must not forget that many of those species occur fre- 

 quently also in our lower horizons. 



A further, although negative proof for our assumption is afforded 

 by the fauna of our Leonard formation (zone of Perrinites.) None 

 of the characteristic Perrinites seems to have been found in the Guada- 

 lupe Mountains. The Perrinites Cumminsi White figured by Girty 

 certainly does not belong to this genus, but in part at least to Waagen- 

 oceras. Nor have there been found in the Guadalupe Mountains any 

 of the very large Producti of the group of Productus sino-indicus 

 Freeh, so common in our Leonard formation. This negative proof is 

 of course not conclusive, but tends to bear out our supposition that the 

 Delaware Mountain beds are younger than our Leonard formation, 

 and contemporaneous with our Word formation. Girty had already 

 found that the fauna from the Glass Mountains collected by R. T. 

 Hill had a great similarity with that of the Delaware Mountain beds. 

 It has to be kept in mind that his collections may have come from dif- 

 ferent horizons and this may at least in part account for the differences 

 Girty found. 



Much more certain are the relations between our fauna and that of 

 some localities on the western border of the great central carboniferous 

 area, developed in Kansas, Oklahoma and Texas. Most of the Per- 

 mian existing in this region has not yielded any ammonoids, but there 

 are somS localities in Texas where ammonoids have been described and 

 where these even seem to be quite plentiful. These are the Old Military 

 Crossing of the Big Wichita in Baylor County ; the falls on Salt Croton 

 Creek, Kent County; Quanah, Hardeman County, and a place near 

 San Angelo, Tom Green County. In the last named locality, only a 



