CARBONIFEROUS 295 



The ISTation Eiver formation has yielded no fossils except a few plant 

 fragments, upon which J\f r David "White has reported as follows : 



"This collection consists of tbi-ee fragments of rock with one counterpart 

 containing small fragments of carbonized wood, decorticated stems, etc. The 

 plant remains bear evidence of transportation, maceration, and trituration, 

 the result being that none of them are definitely determinable, even generic- 

 ally. One fragment, about 1 e. m. in length and G mm. in width, evidently 

 represents a branch of some lepidophyte or gynniosperm. Although it is par- 

 tially decorticated as the result of maceration, so that the epidermal charac- 

 ters are lost, the subepidermal features of this branch so closely resemble 

 those of certain Carboniferous strobiliar axes and earlier types of phyllotaxy 

 that I am inclined to regard it as probably belonging to one of these Paleozoic 

 forms. In fact, though constrained to emphasize the poor condition and lim- 

 ited characters presented by the specimen and the consequent hazard of any 

 attempt at identification, I am nevertheless disposed to regard this fragment as 

 belonging to one of the Carboniferous lepidophytes. Among the latter it bears 

 the closest resemblance to some of the early forms in the basal Carboniferous 

 or the late Devonian." 



The stratigraph)' and the invertebrate faunas of the associated forma- 

 tions strongly support the opinion that the I^ation Eiver coal is of Car- 

 boniferous age. The coal seam occurs near the axis of an anticline, the 

 beds dipping away in opposite directions at angles of 30 to 60 degrees on 

 the north and south sides of the N"ation Eiver valley. South of the river 

 they pass under a massive white limestone carrying an Upper Carbon- 

 iferous fauna and in which a series of open folds is developed along the 

 north side of the Yiikon. Considerable interest attaches to the beds at 

 the Xation Eiver coal mine, because it is the only locality in the Yukon 

 basin where beds of Carboniferous age have afforded coal. 



The uppermost member of the Carboniferous is a white subcrystalline 

 limestone, with a minimum thickness of at least 200 feet, which carries 

 fossils assigned by Doctor Girty to the Upper Carboniferous. This ter- 

 rain was first assigned to the Upper Carboniferous by Schuchert,®* and 

 later placed in the Permian®^ on the l:)asis of ]nore complete collections. 

 It will be shown below that they have been correlated with the so-called 

 Permian rocks of southeastern Alaska and White and Copper rivers ; but, 

 though Doctor Girty is inclined to accept this correlation, he believes 

 that they should all l^e called Upper Carboniferous rather than Permian. 



»*J. E. SpiiiT : Geology of the Yukon gold district. Eighteenth Annual Report, pai'l 

 iii, p. 170. 



"» Arthur .T. Collier: Coal resources of the Yukon. Bulletin no. 218, U. S. Geological 

 Surve.v. p. 16. 



Alfred H. Brooks : The geography and geology of Alaska. Professional paper no. 43, 

 U. S. Geological Survey, pp. 222-223. 



