FAUNAL EVIDENCE AND COREELATION. 223 



series than the familiar Penns^'lvanian Derhya crassa or even the Neo-Mississipj)ian 

 forms. The Seminula present resembles the Chester form S. suhquadrata vaov& than 

 S. sxihtilita, common in the Upper Carboniferous, but the evidence of the present 

 material in its relation to both these species can onlj^ be regarded as slight. Spirifer 

 sj). is of a type which is unknown in our Upper Carboniferous faunas, and one so 

 rare that I am acquainted with but two others similar to it — Spiriferinct acicuh'fera 

 Rowley, which was found at the very base of the Mississippian series, viz, in the 

 Louisiana limestone of the Chouteau group of Missouri, and Spirifer schucherti 

 Rowley, found in the Lower Burlington limestone at Louisiana, Mo. Regarding 

 Emnetriaf sp., as previously stated, if this fossil could be definitel}^ identified as 

 Eu. marcyi or Su. altirostris, the evidence thus afforded would be of considerable 

 moment. As I personally regard the identity of this shell with one or other of the 

 species mentioned as highly probable, I still attach importance to its presence in this 

 fauna. Myalina arlcansasana? seems to be more nearly allied to the Chester form 

 than to any occurring in the Upper Carboniferous, not even excepting Naiadites 

 elongatus. Eiimnphalus cf . speir/enensis has its closest and indeed its onlj^ close allies 

 in the Mississippian series, and I can recall no form in the Upper Carboniferous, 

 and especially no common form, to which it could be referred. The other species of 

 the Leadville have essentially no weight in the present discussion. The intrinsic 

 evidence, therefore, is almost invariablj' in favor of referring the Leadville limestone 

 to the Lower Carboniferous, and its cumulative force is considerable. But the age 

 of the Leadville limestone at Leadville need not be, and indeed should not be, 

 determined independentlv of the Carboniferous faunas of other areas. 



Geographicall}' and in the correspondence of geologic section the Paleozoic 

 deposits at Leadville are closelj" related to those of Aspen. The fauna from the 

 Leadville limestone at Leadville, however, is less similar to that of the Leadville 

 limestone at Aspen or in the Crested Butte quadrangle than to that of the Paleozoic 

 exposures of the Front Range. Indeed, onh' a single species, doubtfully identified, 

 of those at Leadville occurs either at Aspen or in the Crested Butte quadrangle, and 

 but two are found to be common to the Leadville and the San Juan, Crested Butte, 

 and Aspen faunas. As I shall subsequently point out in detail, a much closer relation 

 exists between the Leadville fauna and that of the Front Range Mississippian, and 

 the faunas of this group are rather markedly different from those of central Colorado." 

 Neither can the age in the Mississippian of this typical Leadville fauna be considered 

 apart from the evidence of the related faunas which I have yet to consider. There- 

 fore the discussion of this point will be deferred to a somewhat later and more 

 advantageous place. 



a While these statements are true for the collections in hand, the latter are so scanty and presumably so imperfectly 

 represent the whole fauna that they may not accurately express the real faunal relations. 



