PALEOZOIC CORDILLERAN GEOSYNCLINE 





'assemblage. The western rocks contain some siliceous pyroclastics, which have 

 not been recognized in the other assemblages (Roberts et al., 1958). 



Silurian strata have been recognized in the northern Klamath Moun- 

 tains by Wells et al. (1951), and rest on highly foliated schists which 

 may be metamorphosed Ordovician and Cambrian or Precambrian in 

 age. The Silurian beds had formerly been considered Devonian, but 

 patches of Devonian limestone of undetermined stratigraphic relations 

 crop out nearby. The sequence of units now recognized by Wells and co- 

 workers is as shown in Fig. 6.13, and is compared with the assemblage 

 of rock units in the southern Klamath Mountains. Since no Ordovician 

 or Cambrian beds are yet known west of north-central Nevada, the 

 possibility of correlating the Salmon and Abrams schists with the Ordo- 

 vician and Cambrian is suggestive. The Copley and Chanchellula are 

 questionably correlated with the "Silurian strata" of the northern Klamath 

 Mountains. 



Devonian Basins 



The Devonian basins are in much the same pattern as the Ordovician 

 although the strata are not so thick. The Transcontinental Arch in Utah 

 and Arizona was more widely covered, however (Fig. 6.5). 



Although Devonian strata are found nearly everywhere west of the 

 Transcontinental Arch ( Rrooks and Andrichuk, 1953 ) , they are over 1000 

 feet thick only in the western part of the general Rocky Mountain area. 

 In the Roberts Range, Nevada, Merriam ( 1940 ) has described 4465 feet 

 of Devonian beds, and at nearby Eureka he has found 4000 to 5000 feet 

 of them. They are composed chiefly on limestones and dolomites, their 

 fossil content indicates a rather complete section, and the broad trough 

 in which they accumulated subsided during most of Devonian time. ( See 

 Fig. 6.9.) 



Devonian rocks of the Sulphur Spring and Pinyon ranges have been recently 

 described by Carlisle and others, who showed that northward from the 

 Roberts Mountains the Nevada-Devils Gate sequence thickens, becomes more 

 dolomitic, and less fossiliferous. The sequence contains vitreous quartzite units 

 as much as 400 feet thick that grade into carbonate quartz arenites and thus 

 resembles the Devonian section near Eureka more than the section at Lone 

 Mountain. 



DEVONIAN 



Fig. 6.5. Thickness and paleogeographic map of the Devonian. Antler orogenic belt, Sta 

 bury anticline, and Beaverhead dome made appearance in Late Devonian. Most of sedime 

 are Middle Devonian. 



ns- 



nts 



