24 REPORT UNITED STATES GEOLOGICAL SURVEY. 



CARBONIFEROUS SYSTEM. 



The peculiar characteristics of those groups of strata which are abun- 

 dantly developed in the great Rocky Mountain region, and which have 

 been, by all geologists who have examined them, referred to the Car- 

 boniferous age, leave no doubt as to the correctness of that reference. 

 It is, however, true that the three great divisions of the system, the 

 Subcarbonilerous, Carboniferous or Coal-Measures, and Permian, which 

 are recognized in Europe aud also, in part at least, in the interior region 

 of North America, are not recognizable as such in the western portion 

 of the continent, with the possible exception of the Subcarboniferous 

 division, as distinct from the remainder. There seems indeed to be no 

 good reason why we should expect to find this to be the case, because 

 the marking-off of a system of rocks into groups and formations, as well 

 as the modifications of the then existing forms of life, the remains of 

 which are now found to characterize those formations, was due to the 

 then prevailing physical conditions, and their periodical changes, the 

 former of which we have no reason to suppose could have been universal 

 nor the latter simultaneous in different parts of the world. The coal- 

 making condition, which was remarkably characteristic of the Carbon- 

 iferous age in Europe and Eastern North America, seems not to have 

 existed at all, or only in an exceedingly slight degree, in what is now the 

 great Rocky Mountain region, during any part of this great geological 

 age. During the whole of that age, the deposits there seem to have 

 been wholly marine, and to have been largely formed in comparatively 

 shallow waters. 



The Carboniferous strata of that western region are, it is true, marjjed 

 off into groups, but they are not marked off in the same manner that 

 they are in Europe and Eastern North America ; and there ought to be 

 no strained effort made to require those of the latter regions to corre- 

 spond with those of the former, for they are not separated from each 

 other by similar fauna! and floral differences. There seems to be very 

 little reason to doubt that the whole of the Carboniferous age is repre- 

 sented by the deposits referred to in Western North America, although 

 the types of ^ssils they contain are seldom if ever of such a character 

 as to warrant their distinctive reference to either the Subcarboniferous, 

 Carboniferous, or Permian periods of the age. On the contrary, the 

 types that are relied upon in Europe, and also others that are similarly 

 relied upon in the eastern portion of North America, to prove the Sub- 

 carboniferous age of the strata containing them, are here found intimately 

 associated with an abundance of those forms that are equally charac- 

 teristic of the Carboniferous or Coal Measure period, and even with 

 some of Permian type. Furthermore, the uppermost division of the 

 Carboniferous strata in this far western region, which probably repre- 

 sents in time the Permian Group of Europe, has not, to my knowl- 

 edge, been found to contain a single faunal type that is in any proper 

 sense characteristic of the Permian period as distinct from the Middle 

 or Coal-Measure period. Therefore, in this report at least, I shall make 

 no attempt to refer any of the Carboniferous strata of this great region 

 to either of the three divisions originally established for the system ; 

 but I shall regard all the groups that have been named in the foregoing 

 sections and elsewhere in this report as purely stratigraphical divisions, 

 and probably inseparable from each other on paleontological grounds. 

 This statement will explain why so little reference is had to paleonto- 

 logical characteristics in the following account of the Carboniferous 

 groups. It is proper to mention, however, that from somewhat restricted 



