THE BANNOCK OVERTHRUST 6095 
assemblage of small forms more or less related to the ““Spergen”’ fauna reported 
by Meek from Ross Fork. The horizon of all these rather strikingly different 
facies appears to be below that of Station rot. 
IOI 
Zaphrentis sp. Edmondia ? sp. 
Stenopora sp. a Conocardium sp. 
Stenopora sp. b Schizodus sp. 
Stenopora ? sp. Sphenotus sp. 
Batostomella ? sp. Myalina aff. Sanctiludovici 
Rhombopora ? sp. Leptodesma aff. Spergenense 
Productus semireticulatus » Sulcatipinna Ludlowi ? 
Productus semireticulatus var. Parallelodou ? sp. 
Productus pileiformis Cypricardinia ? sp. 
Productus punctatus var. Aviculipecten sp. a 
Productus aff. longispinus Aviculipecten sp. b 
Diaphragmus elegans Aviculipecten sp. c 
Camarophoria Wortheni Pseudomonotis ? sp.. 
Dielasma sp. Laevidentalium venustum ? 
Spirifer striatus ? Naticopsis sp. 
Spirifer increbescens ? Straparollus similis var. 
Spiriferina sp. Bulimorpha aff. elongata 
Composita trinuclea ? Griffithides sp. 
Edmondia sp. Phillipsia sp. 
THE BANNOCK FAULT 
The field seasons of 1909 and roro led to the recognition by 
members of the U.S. Geological Survey of important thrust faults 
in southeast Idaho (rod, e) and adjacent parts of Utah (1of, g). 
In tort the study of the great fault east of Georgetown, Idaho, led 
to the view that several of these faults, formerly considered distinct, 
are in reality parts of one great overthrust, for which the name 
Bannock is proposed, from Bannock County, Idaho, where the 
fault is strikingly developed. The individual faults which have 
been thus united and the facts upon which the interpretation rests 
are described below (Fig. 1). 
GEORGETOWN FAULT 
In 1909 a thrust fault involving the superposition of Missis- 
sippian limestones upon rocks of Jurassic or Cretaceous age was 
recognized by Gale (10d) in Georgetown Canyon about 5 miles 
