80 INVERTEBRATE PALEONTOLOGY. [WHITE. 



those strata. These two belong to the two genera respectively Archimedes 

 and AmplexuSj the former of which, especially, 'has been regarded as an. 

 exclusively Subcarboniferous genus; and yet they are found in the Lower 

 Aubrey Group, nearly three thousand feet above the base of the Carbonifer- 

 ous series, and also above, and mingled with, types that have not hitherto 

 been found in strata so low as the Subcarboniferous 



Few or none of the fossils of the collections are of such a character as 

 to suggest the Permian age of the strata from which they were obtained, 

 not even those of the Upper Aubrey Group. I have elsewhere shown* 

 that the prevalence of certain types which have been relied upon to prove 

 the Permian age of the strata containing them may be due to peculiar 

 physical conditions, and I therefore regard it as not improbable that the 

 time of the Permian period may be represented in the Plateau Province 

 by the Upper Aubrey Group, although the distinguishing types are want- 

 ing there. In view also of the mixture which we find, of "Carboniferous and 

 Subcarboniferous types in the same strata, it seems probable that the time 

 of the whole Carboniferous age, including its three periods, Subcarbonifer- 

 ous, Carboniferous, and Permian, is collectively represented by the four 

 groups recognized in the Plateau Province. 



It seems probable, therefore, that, although some localities in Nevada 

 and Montana have furnished collections of almost exclusively Subcarbonifer- 

 ous types, we shall not, as a rule, be able to define in this region, the three 

 periods into which the age is divided in other parts of the world. It seems 

 also probable that no divisions of the Carboniferous strata of the Plateau 

 Province can be made that will represent geological periods, well defined 

 upon paleontological grounds, either corresponding to those already estab- 

 lished in other parts of the world, or differing from them. 



MESOZOIC AGE. 



TRIASSIC PERIOD. 



Some small collections of fossils which possess peculiar interest were 

 collected by Mr. E. E. Howell, in 1874, from the following localities in Utah: 

 At Toquerville ; Virgin River, south of Toquerville ; near Workman's 



* Geology of Io\vn. 1870, vol. i, page 24'J, 



