34 CAKHONll-'KKnrs FORMATIONS AND KAUNAS OF COLORADO. 



'i'ho lowor Auhroy group t'unii.shod most of tlu' fossils collected, and an extensive 

 fauna is cited, obtained ehielly at three localities. One of these is not far from the 

 stations at wiiieli the Red Wall fossils were found. The two others, Echo Park and 

 Split Mountain Canyon, are close together in the Uinta Mountains in the extreme north- 

 eastern ])art of rtah. From Echo Park are cited Amplexuszaphrentiformis, Fenestella 

 .sp., Archimedes sp., CJionetes platynotus, Prodaictus longispinus (?), Preductus 

 costatm (^), /•*. coatat'us var., Productus muricatus^ Hemip^'onites crenlMria, Semimda 

 suhtiUta, Sjjirife^' rockymontanus, and PhiUij>sia sp. ; and from Split Mountain 

 Canyon are cited Amplexus zaphrentiformis, Chsetetes milleporaceiis, Acertmlaria sp. , 

 and Spirifer roehymontcmus. It thus appears that two of the four species collected 

 at Split Mountain Canj^on occur also at Echo Pai'k, and there seems to be no reason 

 for suspecting that the two lists do not represent the same fauna. The specimens 

 upon which some of the listed species were based appear to have been lost from the 

 collection, and while I do not agree in every case with Professor White's identifica- 

 tions, I think the fauna shown, whether by the lists or by the specimens themselves, 

 must be taken as indicating Upper Carboniferous. On the other hand, the 

 assemblage is not quite that of one of the common Upper Carboniferous faunas of 

 the Mississippi Valley, so that to a certain extent Powell's statement is borne out — 

 that in the Great Basin region thegTouping of fossils is peculiar (loc. cit., p. 4). It is 

 with this fauna that there is said to occur the anomalous association of Lower 

 Carboniferous types, such as Amplexus zaphrentiformis and the genera LitJiostrotion, 

 Acervularia, and Archimedes, with an Upper Carboniferous fauna, a fact to which 

 attention was directed by White in a passage previously quoted. The survival into 

 the Upper Carboniferous of the already long^established genus Afiij^lexus, which is 

 known in America as late as Upper Mississippian time, would not necessarily 

 occasion surprise, nor even possibly that of the Devonian genus Acervularia, which 

 is also known in the Carboniferous, but the case is somewhat different with 

 Archimedes. A striking and highly specialized scion of the fenestellid stock, this 

 type makes its earliest appearance in the Keokuk epoch; it attains its maximum in 

 the Chester, and has never before, I believe, been cited in association with an Upper 

 Carboniferous fauna. For my own part, I should wish to see the occurrence verified 

 in the present case, and am even inclined to invoke an accidental, or some other 

 than an actual faunal. association. Unfortunatel}', and the circumstance may not 

 be without significance, the representatives of both Archimedes and Acervularia are 

 missing from the collection as it now stands. 



On the other hand, as the Lower Carboniferous is supposed to be missing in the 

 eastern Uintas, the whole Paleozoic section above the Uinta sandstone being referred 

 to the Upper Carboniferous, if these specimens of Archimedes really were obtained 

 from this area and from beds now in place, it .seems that the peculiar association 



