Schuchert — Carboniferous of Grand Canyon of Arizona. 355 



Fort Defiance, of Walchia pinniformis, W. gracilis, and 

 W. hypnoides(f). These plants White states are charac- 

 teristic of the Permian, and are present in Oklahoma and 

 in the Wichita formation of Texas. 



It should be noted that these fossils are found immedi- 

 ately above a marked erosional unconformity. If there- 

 fore we give full significance to this unconformity and 

 with it bolster up White 's provisional conclusion as to the 

 age of the plants, the upper 290 feet of the Supai are to be 

 referred to the Permian system. The question then is 

 raised, What is the age of the rest of the Supai that is 

 900 feet in thickness? That it is younger than early 

 Mississippian is clear, and that it is at least as young as 

 Pennsylvania?! is also probable, as will be shown later 

 on. On the other hand, the sedimentary character of the 

 entire Supai is strikingly similar. Doctor Noble has 

 determined what the writer did not see at the time of 

 collecting the fossils above mentioned — that beneath the 

 fossiliferous zone is "locally one of the clearest discon- 

 formities in the canyon, a counterpart of that at the base 

 of the Devonian. The red shales that have the plant 

 remains lie in little hollows or troughs eroded in the 

 upper cliff-making Supai sandstone. In places the 

 knolls of sandstone rise 50 feet above the base of a 

 hollow. I traced the unconformity for half a mile or 

 more around the head of Hermit Creek to make sure, and 

 then accepted it as a fact. The fossils occur only at the 

 base of a hollow. I have crossed the Supai many times 

 in widely separated parts of the canyon and have never 

 seen a sign of a fossil plant in it before. Perhaps it is 

 only in the places where this disconformity is so well 

 developed that they can be found. The plants appear to 

 have been washed into these hollows and concentrated 

 there." The following diagram (fig. 3) shows the dis- 

 conformity as determined by Noble. 7 Noble thinks that 

 if further study reveals the presence of the disconformity 

 in other parts of the Grand Canyon, it may be possible to 

 separate the Supai into two distinct formations. "Above 

 the break the rocks are all red shale and shaky sandstones 

 to the base of the Coconino. Not only this, but the red 

 shaly member increases decidedly in thickness to the 

 westward. On the Hermit trail it is 290 feet thick, and 

 in the west end of the adjoining quadrangle, the Shinumo, 



7 Unpublished manuscript in preparation for the U. S. Geological Survey. 



