528 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Nannites, Ussuria, Pseudosageceras, Hedenstroemia, Cordillerites, Tirolites, and Proptychites 

 most of which are represented by closely related species in the Lower Triassic of India and 

 Siberia. 



The Middle Triassic occurs chiefly in Nevada and southeastern California. In the Inyo 

 Range, southeastern California, about 200 feet of shaly limestones contain the following genera 

 characteristic of the lower horizon of the Middle Triassic: Acrochordiceras, Xenodiscus, Hun- 

 garites, Ptychites, Tirolites, Ceratites, and Parapopanoceras. 



In central Nevada, in the West Humboldt Range, the higher beds of the Middle Triassic 

 are represented by about 800 feet of shaly limestones, in which the most characteristic genera 

 are Ceratites, Anolcites, Dinarites, Danubites, Celtites, Hungarites, Beyrichites, Acrochor- 

 diceras, Balatonites, Eutomoceras, Ptychites, Joannites, Lecanites, and Atractites among the 

 cephalopods, Daonella among pelecypods, and Cymbospondylus among vertebrates. 



The Upper Triassic is best represented in northern California, where the Hosselkus lime- 

 stone and the shales below and above this formation contain characteristic fossils. The Hossel- 

 kus limestone and the interbedded shales have a thickness approximating 500 feet. Fossils 

 are very abundant throughout this formation, although much better preserved near the base. 

 The best known fauna belongs to the zone of Tropites subhuUatus, and contains as its most 

 important members the following genera: Tropites, Paratropites, Discotropites, Juvavites, 

 Sagenites, Leconteia, Trachyceras, Clionites, Arpadites, Polycyclus, Metatirolites, Hauerites, 

 Dieneria, Arcestes, Paraganides, Proclydonautilus, Cosmonautilus, and Atractites among 

 cephalopods, Halobia among pelecypods, and Shastasaurus among the vertebrates. 



Above the Hosselkus limestone lie the Pseudomonotis slates, of unknown thickness, charac- 

 terized by Halorites, Rhabdoceras, Arcestes, and Pseudomonotis. 



In the West Himiboldt Range in Nevada the Star Peak limestone, about 1,200 feet thick, 

 appears to represent the Hosselkus limestone, although very few fossUs have ever been found 

 in it. Above the limestones lie the Pseudomonotis beds, about 800 feet of shales and shaly 

 limestones, in which are found Pseudomonotis suhcircularis, Rhabdoceras, Halorites, Placites, 

 and Arcestes, an association characteristic of the Noric horizon. 



K 12. SOUTHEASTERN IDAHO. 



Peale and White first described the probably Lower Triassic rocks of south- 

 eastern Idaho occurring in the Blackfoot Basin near John Grays Lake, in latitude 

 43°, longitude 111° 30'. Peale «'" gives the following section: 



General section of Jura- Trias in southeastern Idaho and western Wyoming. 



I 





"5 p-^ 



5. Eed and gray shales with green sandstones and irregular greenish arenaceous limestones at the 

 top. Thickness, 700 feet. 



4. Laminated limestones, blue at base, passing into gray at top, succeeded above by grayish cal- 

 careous shales; many of the layers are probably arenaceous. Thickness, 800 feet. 



ffl 



Red quartzitic sandstones with shaly arenaceous and calcareous layers at the base of the 

 section. These are probably the equivalent of the typical " red beds " of the Eastern Rocky 

 Mountains. Thickness, 1,000+ feet. 



0*0 



2. Alternations of reddish and greenish sandstones and arenaceous and calcareous shales with blue 

 and gray limestones, generally laminated. Thickness, 3,000+ feet. 



These with No. 1 are the beds of the section given in Dr. White's paper (as that of locality No. 1). 

 The beds are fossiliferous at four horizons, containing species of anew Triassic (?)genus named 

 Meekoceras by Prof. Hyatt, together with forms that have been heretofore regarded as of 

 Jurassic age. 



Carboniferous (?). 



Massive grayish-blue limestone, overlain by quartzite and dark-blue laminated limestones. 

 Thickness, 1,200+ feet. 



