210 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Foi.V. 



i'ox: known exeeptious to this rule, and which have just been referred to, 

 the strata are understood to be at or near the base of the great Carbon- 

 iferous series. It is also true that, as a rule, the Devonian and Upper 

 JSilurian series are absent in all that great region, and it may therefore 

 be properly suggested that at those places where characteristic Subcar- 

 boniferous fossils are not present in the Carboniferous strata, the fuR 

 Carboniferous series is not there complete; and that the Subcarbonifer- 

 ous, Devonian, and Upper Silurian strata are all absent from one and the 

 same cause, or from similar causes. 



The instances which have just been cited of the discovery of a Sub- 

 carboniferous fauna at several localities in that great Western region, 

 if considered without reference to other facts, would seem to prove 

 conclusively the existence of strata there which represent the Subcar- 

 boniferous period as distinct from the succeeding portion of the Carbon- 

 iferous age; but a number of facts already known tend to support an 

 opposite opinion. Tor example, several types of invertebrate fossils 

 that are elsewhere known only in Subcarboniferous strata have been 

 found at various localities in that region in strata which are evidently 

 higher in the series than we may reasonably suppose the highest Sub- 

 carboniferous strata to reach. Moreover, some of these types at least 

 are, in the Western Territories, not only intimately associated with types 

 which characterize the Coal-measure strata further east, but some of the 

 fossils of the latter types are specitically identical with characteristic 

 Upper Coal-measure forms of the Mississippi Yalley. In other words, in 

 different i)ortions of the Western Territories there is found to be an 

 unmistakable commingling of Subcarboniferous and Upper Coal-measure 

 types in the same strata. Besides this, so far as I am aware, no geologist 

 who has examined any part of that great region has ever discovered or 

 suggested the existence of a x)lane of demarkation between the Subcar- 

 boniferous and Coal-measures corresponding with that which separates 

 the two groux)s in the Mississippi Valley. 



In this paper three of the Subcarboniferous types just referred to will 

 be noticed, namely, Archimedes^ Leptopora, and Grmiatocrinus. Besides 

 the representatives of these genera, there are among the collections 

 brought in by Prof. St. John from Southeastern Idaho some fragments 

 of a tSijirifer of the Syringothyris type^ and one or two species of Acervu- 

 laria. The former type has not yet been found in other American strata 

 at a higher horizon than the Subcarboniferous, and the latter genus is 

 almost equally characteristic of the same group in the Mississippi Valley,, 

 although in the Western Territories it is found associated with Coal- 

 measure types. 



Some geologists have recognized the Permian division as a separate- 

 grouj) of the great Carboniferous series in the Western Territories; but 

 it is safe to say that while certain of the uppermost strata of that series, 

 probably rei^resent the time of the Permian period, the invertebrate 

 fauna of those strata, so far as it has yet been investigated, aftbrds no 



