RECAPITULATION OF PALEOZOIC FORMATIONS. 171 



apparently represented in the Colorado sediments. The chronological point at 

 which this elevation took place is, except in a general way, unknown. It may 

 have occurred soon after the formation of the Leadville limestone, the absence of the 

 upper Mississippian horizons being due not so much to erosion as to nondeposition; 

 but it seems to me rather more probable that this episode was nearly contemporaneous 

 with the elevation in eastern North America at the close of Mississippian time. That 

 the elevation is of wide extent is indicated by the absence over such large ai'eas in 

 our Western States of upper Mississippian faunas. To the erosion which resulted 

 from this elevation the variation in thickness of the Leadville limestone in different 

 sections can often be ascribed. When subsidence again permitted the formation of 

 sediments, the earliest deposits were f requentlj^ of a less purely marine character, 

 and shortlj' a great thickness of sands and conglomerates intermingled with non- 

 persistent limestone bands began to form over great areas in the State. 



The Paleozoic section of central Colorado, by which term I would include the 

 Grand River, Elk Mountain, and South Park areas, is singularh' uniform, and this 

 is scarcely less true of the strata of Carboniferous age than of the earliei' Paleozoics. 

 Though these are fairly constant in lithologic characters, the nomenclature emploj^ed 

 for them has varied somewhat. Thus in the Anthracite-Crested Butte folio the 

 Carboniferous formations are called the Leadville limestone, Weber limestone, and 

 Maroon conglomerate; in the Aspen monograph, the Leadville limestone, Weber 

 formation, Maroon formation, and the Triassic;" in the Tenmile folio, the Leadville 

 limestone, Weber shale, Weber grits, Maroon formation, and Wyoming formation ;<* 

 and in the Leadville monograph, the Blue limestone, Weber shale, Weber grits, and 

 Upper Coal Measures. 



The distribution of the Leadville limestone has already been described. While 

 the general equivalence of the Upper Carboniferous formations of this area is 

 comparatively easj' to ascertain, their relations to the dijfferent formations of the 

 regions adjacent, of the Uinta Mountains, of the Front Range, of the Sangre de 

 Cristo Range, and of the San Juan region are questions of more intricacj', and it 

 will not be possible to consider each formation by itself, but in relation to the other 

 Pennsylvanian formations of the same section. 



In the Crested Butte quadrangle the beds immediately overlying the Leadville 

 limestone are called the Weber formation, and they are succeeded by the Maroon 

 formation. The Weber formation apparently derives its name from the Weber 

 quartzite of the Wasatch Mountains of Utah. I shall refer to this point again, but 

 it seems that the correctness of the correlation suggested by the nomenclature is very 

 doubtful and that the employment of the term Weber for formations in Colorado 

 can not with propriety be continued. The Weber formation consists principall}^ of 



1 1 do not nf course mean to imply that the Triassic ot the Aspen district and the Wyoming formation are Carboniferous 

 formations, but 1 desire to consider them in connection with the Carboniferous and to compare their nomenclature. 



