G. B. Richardson — Paleozoic Formations. 479 



while others are dark, and the two parts of the formation 

 can not always be distinguished lithologically. The zone 

 which carries the most abundant Richmond fossils in places is 

 seamed with conspicuous bands of chert a few inches in thick- 

 ness. In the Van Horn quadrangle the base of the Montoya 

 limestone is commonly marked by the presence of thin- 

 bedded earthy yellow and reddish limestone, but otherwise in 

 both quadrangles the contact is apparently conformable. Like 

 the El Paso [limestone, the Montoya is characteristically mag- 

 nesian. Mr. Ulrich has identified the following fossils from 

 the Montoya limestone : 



Fossils from the Galena beds. 



Peceptaculites oweni. Hormotoma major. 



Maclurina manitobensis. Ormoceras sp. undet. 



Maclurina acuminata. 



Fossils from the Richmond beds. 



Streptelasma rusticum. Dinorthis proavita. 



Ilemiphragma imperfectum. Platistrophia acntilerata. 



Monotryprella quadrata. Phynchotrema capax. 



/Strophomena flexuosa. Orthis whitfeldi. 



Leptwna unicostata. Parastrophia divergens. 

 Dinorthis sabquadrata. 



In southwestern United States outside of the areas here 

 considered few Ordovician rocks are known. The system ap- 

 parently is not represented by sediments in either the Grand 

 Canyon or Bisbee districts. The Longfellow formation in the 

 Clifton quadrangle, Arizona, probably should be correlated 

 with the El Paso limestone as well as a part of the Ordovician 

 limestone in the central Texas region. Recently several 

 small areas of Ordovician rocks have been reported in cen- 

 tral New Mexico by Gordon and Graton.* Mr. Ulrich 

 reports that the Beekmantown fauna of the El Paso limestone 

 is of the type prevailing in the Wichita Mountains, Oklahoma, 

 in the upper 1,000 feet or so of the Arbuckle limestone ; and 

 that the Galena and Richmond fauna of trans-Pecos, Texas, 

 are similar to those in the Mississippi valley, Oklahoma, the 

 Black Hills, the Big Horn Mountains, and elsewhere. 



Silurian. 

 Fusselman limestone. 



The Silurian system in trans-Pecos Texas is represented only 

 in the El Paso region, where the Fusselman limestone outcrops 

 in the Franklin and Hueco Mountains. This is a massive 



* This Journal (4), xxi, p. 190. 1906. 



