66 



CHESTER R. LONGWELL 



recognized as Devonian, Mississippian, and Pennsylvanian. The 

 lowest horizon at which fossils were found lies nearly i,ooo feet 

 above the base of the series, and therefore a part of the lower beds 

 may belong to periods older than the Devonian. At the top of the 

 block an unknown thickness of the Pennsylvanian beds has been 

 removed by erosion. Outside the borders of Callville Mountain the 

 oldest strata exposed are the upper part of the Supai formation, 

 which is mapped (Fig. i) with the Permian. Thus there is a gap of 

 undetermined value in the stratigraphic succession. The following 

 table summarizes the nature of formations and shows their relation- 

 ships : 



