2'28 CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



thai Ihc oriy'iiial liowldcrs were siliceous or fliortv, in which material all our fossils 

 belonging (o the faunas nieulioiied ar(> j)res(>r\('.d. 



SUMMARY. 



The Lower Carboniferous faunas of Colorado can l)e separated on intrinsic 

 o\"idence into two i^'roups, the first of which embraces those from the Ouray limestone 

 of the San Juan region and the Leadvillc limestone of the Crested Butte, Aspen, 

 and Salida localities; the other embraces those from the Leadville limestone at 

 Leadville, the Millsap limestone of CaiiA'on, Garden Park, and Perry Park, and the 

 Eed Beds congiomerates near the northern border of the State. Where small col- 

 lections are made at different points from a large and varied fauna it would follow 

 that comparatively few species would be common to any two of them. This seems 

 true, both as to condition and result, of our Mississippian collections from Colorado. 

 On the whole, however, both groups of faunas show considerable homogeneity. 

 The chief question is how far they are distinct from each other. The fauna of the 

 San Juan and Crested. Butte collections is clearh" that which has several times been 

 described from the Wasatch limestone of Utah and the Madison limestone of the 

 Yellowstone Park and Montana. It occurs also in the Chouteau limestone of 

 Missouri and the Waverly group (Cu_yahoga shale) of Ohio, and its geological age is 

 probabl}^ chieflj^ upper Kinderhook and lower Burlington. It may at least safely be 

 asserted that it is older than the Genevieve period. The fauna of the other group 

 of localities has a more unusual facies. Considering the meager character of the 

 collections, this fauna is rather unusually homogeneous. The faunas from Garden 

 Park and ('anj'ou are practically identical. Five of the eleven species found at Perrj^ 

 . Park occur also in Garden Park, and these iive include the abundant species. Four 

 of the seven species from the Red Beds conglomerate occur at Perry Park or at 

 Garden Park. Five of the nine species found at Leadville were obtained in the Front 

 Eange beds, and only two occur in the far more abundant faunas of the San Juan and 

 Crested Butte regions. At the same time, though the Leadville fauna is much more 

 similar to those of the Front Range than to those of central and southwestern 

 Colorado, there are certain well-marked peculiarities, as, for instance, the abundance 

 along the Front Range of Oransena suhelliptioa var. hardingeiisis, which is not known 

 at Leadville. The Front Range group of faunas, therefore (including- Leadville), is 

 rather peculiar — to what extent maj^ be gathered from the fact that from a total of 

 nineteen species but four occur in the San Juan and Crested Butte group, the resem- 

 blance being especially with the faunas of the San Juan region. The fossils at Can- 

 3'on, Garden 'Park, and Perry Park occur in cherty bands or nodules, bright red on 

 the outer surface, but whitish, purplish, or buff within. From their occurrence and 

 preservation there is reason to believe that the impressions from Larimer Count}^ 

 were made from chertv bowlders. Most of the Leadville fossils occur in siliceous 



