44 



C. R. Longwell — Geology of 



Thickness 

 (In feet) 



Varlaufl allirTial deposits 



Unconfornitty- 



Tertiary 



Saline clays, silt, and sand 



Unconformity 



Horse Soring foimatlon 

 Overton fangloraarate 

 Great Unconformity 



(Equinalcnt to ) 

 Cross-bedded sandstone (the LaPlata) 



liosozoiQ 



Chlnlo format ion 

 Shinanuap conj^lonerite 



Disconformity • 



r.oonkopi formtion 

 Dlsconfomity 



Pennsyl- 

 vnnlan 



Kississlp- 

 plan 



Devonian 

 (and older? 



Cambrian 

 (and lator) 



Kalbab limestone 



Coconino sandstono 



Supai sjmdstone — — 



Mot exposed. UnknovTn thicrtaesB 



Cnllville linestone 

 (Ho anconformity observed) 



Bluepoi.it limestone 



Rogers Spring formation 

 Disconformity 



Uuddy Peaks li-cstane 



Sandstone, quartslte, shale, and 

 linestone. In Virgin Jtountalns. 



1000-2800 

 20-3500 



800-3200 

 10- 200 



400- 700 



0-75 



- lOCOH 



900d 

 6C0^ 



Bocks of the Virgin Mountains. 



Exposures of pre-Cambrian rocks occupy large areas 

 both north and south of St. Thomas Gap. The rocks are 

 schists and gneisses, injected with coarse-grained gran- 

 ite. Above these crystalline rocks lie 70 to 100 feet of 

 red arkose, 150 feet of gray quartzite and sandstone, 

 several hundred feet of greenish shale, and limestones 

 thousands of feet thick. The limestones are in large 

 part Pennsylvanian, Mississippian, and Devonian, but 

 probably the Ordovician and Cambrian periods are also 

 represented. The clastic sediments at the base probably 



