HINTZE, GEOLOGY OF WASATCH MOUNTAINS, UTAH 141 



STRATIGRAPHY 



(i) The major part of the great quartzite and slate series exposed in 

 Big Cottonwood Canyon is Algonkian and possibly Lower Huronian in 

 age. 



(;) The Lower Cambrian is separated from the Algonkian by a heavy 

 basal conglomerate of widespread occurrence. The Cambrian strata of 

 the central Wasatch belong to the lower and middle divisions of the Cam- 

 brian system and are less than one thousand feet thick. 



(k) Above the known Cambrian are about 500 feet of unfossiliferous 

 limestones and calcareous shales provisionally referred to the Ordovician. 

 Silurian strata are entirely wanting in the Cottonwood region. 



(I) Middle and Upper Devonian horizons are represented by what ap- 

 pears to be an unbroken succession of limestones carrying faunas closely 

 allied to those found in western Colorado and Iowa. 



(m) The Devonian beds rest with disconformity upon the lower lime- 

 stones and are separated from them by a thin bed of conglomerate com- 

 posed of limestone pebbles. 



(n) The Mississippian follows the Devonian conformably and is repre- 

 sented by limestones of Lower and Middle Mississippian age which are 

 separated by a continental formation. 



(o) In the Cottonwood region^ there is an unconformity between the 

 Mississippian and the Pennsylvanian (Weber quartzite) which follows, 

 representing a considerable erosion interval. The thinning of the Weber 

 quartzite is probably to be accounted for by overlap upon this erosion 

 surface. 



(p) The Wasatch limestone of the Fortieth Parallel geologists em- 

 braces strata of Ordovician, Devonian and Mississippian ages. The 

 Ogden quartzite and Ute limestone of supposed Devonian and Silurian 

 ages respectively have no existence, as originally defined, in the central 

 Wasatch. 



STRUCTURE 



(q) In the vicinity of Alta there is a great overthrust, presumably 

 from east to west; the overthrust block consists of beds ranging in age 

 from Algonkian through the Paleozoic and Mesozoic; the underthrust 

 member consists of Devonian and older beds. 



(r) The age of the overthrust is probably the same as the main fold- 

 ings of the Wasatch, generally assigned to the end of the Cretaceous. 



