294 BROOKS AND KINDLE PALEOZOIC ROCKS OF UPPER Yt KOX 



"I have been uuable to trace the affinity of this fauna with a member of tlie 

 Russian section, but presumably it is somewhere near the age of the Pioductiis 

 gil/aiiteus zone, in which case a gap of considerable extent separates this from 

 the Upper Carboniferous fauna described below. The fauna of the Calico 

 Bluff section appears to be related to that of the upper part of the Mississip- 

 pian section as developed to the south and west of the typical area. I refer to 

 the Spring Creek limestone and Marshall shale of Arkansas and the Cauey 

 shale of Indian Territory (and probably the Eureka shale of Nevada), which 

 from available data appear to represent the upper portion of the typical Missis- 

 sippian section. This relationship of the Alaskan fauna I believe to be a real 

 and not a fancied one, and while belonging distinctly with the fauuas just 

 mentioned, rather than with the typical Osage and Kinderhook, it would at 

 present be unsafe to say that these localities represent the upper Mississippian 

 alone." 



Since the preceding observations of Doctor Girtj' indicate that the near- 

 est faunal equivalents of tlie Calico Bluff fauna in the United States are 

 representatives of the upper portion of the Mississippian section, it 

 should be pointed out that all of the available stratigraphic evidence indi- 

 cates that it is the earliest Carboniferous fauna present in the Yukon 

 section. The stratigraphic evidence appears to place it somewhat lower 

 than the faunal evidence and to indicate that it represents both the upper 

 and the lower portions of the ^Mississippian section. 



A section about 2 miles above the mouth of Seventymile river, on the 

 opposite bank of the Yukon, exposes the Carboniferous series seen at 

 Calico bluff and some higher beds which show the Lower Carboniferous 

 shales terminated by a coarse conglomerate which, with some interbedded 

 shales, is about 200 feet tliick. This conglomerate may represent the 

 base of the JTation Eiver series. The limestones and shales here show 

 about the same association of species as in the Calico Bluff section. 



The Xation Eiver series includes about 3,700 feet of gray clay shales, 

 with some clay slates interpolated with heavy beds of conglomerate and 

 some sandstone. It is typically exposed along Xation river, where it 

 includes some small seams of bituminous coal. The limits of this forma- 

 tion are well defined. The base is believed to be marked by an uncon- 

 formity which separates it from the shales and limestone of the Calico 

 Bluff formation. At the top it is limited by the heavy limestone which 

 previously formed the topmost member of the Carboniferous and will l^e 

 described below. 



Two conglomerate beds are particularly striking in this formation. 

 One occurs at the base and is very massive, and the second, which is not 

 quite as heavy, occurs about 1,000 feet above the l)ase. The succeeding 

 thousand feet is largely made up of shales, with some fine conglomerates 

 and sandstone, while the upper 500 feet of the formation is chiefly gray 

 shales. Some bituminous coal beds occur in the lower part of the section. 



