116 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Tertiary 
Cretaceous 
Jurassic 
Upper 
Triassic 
Lower 
Shinarump 
Permian 
Upper 
Aubrey 
Lower Carboniferous 
Red Wall 
Devonian 
Tonto shales 
Cambrian 
Tonto sandstone 
Unkar and Chuar Algonkian 
Archean ? . 
Figure 2. 
Columnar section of formations in the Grand canyon district. 
