492 H. W. SHIMER PERMO-TRIASSIC OF NORTH^VESTERN ARIZONA 



is Terr similar to the PennsylYaniaii fauna of Kansas. These two faunas 

 are compared in parallel columns by A. B. Eeagen,^® with the conclusion 

 that out of 36 genera from this ^Tipper Eedwall*^ 32 occur in the Kansas 

 Pennsylvanian, and of the 32 species from the former 26 are also found 

 in the latter. 



Between the Supai, delimited as above, and the Eedwall occurs a dis- 

 conf ormity, representing the time of the upper Mississippian and portions 

 of the middle Mississippian and lower Pennsylvanian. This makes the 

 Pennsylvanian begin in this region with the deposition of the lower 

 Supai beds after the land period represented by this erosional interral. 



SUPAI (UPPER) 



According to David "White, in a letter to Schuchert/' the few fossil 

 plants found in the upper Supai indicate a lower Permian age, or at 

 least an age not lower than the highest Pennsylvanian. These red beds 

 of the upper quarter of the Supai formation are separated from those of 

 the lower three-quarters by a disconformity. 



COCOXIXO SAXDSTOXE 



With the exception of rare amphibian footprints/^ no fossils have been 

 reported from the Coconino sandstone — -a gray to white, strongly cross- 

 l^edded formation. It is disconformably separated from the Supai be- 

 neath. 



KAIBAB LIMESTONE 



The Kaibab limestone formation consists of rather thin-bedded, more 

 or less siliceous limestones, including as a medial member one or two 

 hundred feet of gypsiferous red shales and sandstones. 



One of the most noticeable peculiarities of the Kaibab fauna is the 

 absence of true Spirifers. Such characteristic, abundant and wide-spread 

 species of the typical American Pennsylvanian as Spirifer rocky montanus 

 and S. cameratus are wanting here. At the same time pelecypods, 

 especially of the genera Pseudomonotis and Bakewellia, increase in 

 relative abundance. These differences similarly distinguish the Permian 

 from the Pennsylvanian in Kansas. ^^ Concerning the correlation of the 

 Kaibab limestone, Girty^° later concludes that its fauna ''contains a num- 

 ber of species which are very similar to, or identical with, species that 

 occur in the G-uadalupian fauna, . . . and it seems less improbable 



i^Centralbl. f. Mineral.. 1907. pp. 609-611. 



1" Op. cit.. p. 354. 



IS Schiichert : Op. cit, p. 350. 



19 G. H. Girty : U. S. Geo!. Survey, Bull. 211, 1903. pp. 73-83. 



20 L. F. Noble : U. S. Geol. Surrey, BuU. 549, 1914. p. 71. 



