CARBONIFEROUS UNDIVIDED. 395 



be the equivalent of some of the upper lava flows referred to the Carboniferous in Wliite River 

 valley. Proof for this correlation is lacking and will remain so until the upper limit of the 

 Carboniferous is determined, but the seeming transition, without interruption, from Carbon- 

 iferous to Triassic deposits in the Yukon VaUey suggests the possibility of such a condition 

 holding at the head of White River and that an unconformity between Carboniferous and Triassic 

 deposition may not occur there. Wliether the volcanic beds occurring between the massive 

 limestones of the Wliite and Chitina vaUeys should be referred to the Carboniferous or Triassic 

 may be difficult if not impossible to determine. 



Q 3. SEWARD PENINSULA, ALASKA. 



Carboniferous limestone has been recognized in Seward Peninsula at Cape 

 Mountain, near York;" at Baldy Mountain, in the Kougarok mining district;* at 

 Cape Deceit, in Kotzebue Sound;" and at Black Mountain, on the lower part of 

 Fish River'' — in other words, at widely separated localities throughout the penin- 

 sula."° There is strong reason for believing that in addition to these known mapped 

 localities some of the areas of limestone in the "unclassified Paleozoic" of Seward 

 Peninsula may be of Carboniferous age. In 1909 fossils of either Devonian or 

 Carboniferous age were found by Smith and Eakin^"^ in dark-colored limestones 

 on the eastern flanks of the Darby Range at several places. Other limestones 

 associated with schists having characters similar to those of the known Carbon- 

 iferous areas apparently occur in many places in northeastern Seward Peninsula. 

 In 1908 a very poorly preserved fossil from the large limestone area west of 

 Casadepaga River suggested possible correlation with the Carboniferous. 



From the wide distribution of Carboniferous rocks in the peninsula it is probable 

 that many infolded and infaulted remnants occur in such relations to the other 

 members that the structural relations are obscure and involved. All of the known 

 Carboniferous has been subjected to deformation, and in some places it has been 

 intruded by igneous rocks of the granite family, so that under ordinary circum- 

 stances fossils are lacking and the original characters are more or less obliterated 

 by secondary structures. 



0, 7. UPPER YUKON AND PORCUPINE RIVERS, ALASKA. 



Brooks and Kindle, ^"^ who examined the Porcupine- Yukon section in 1906, 

 distinguish the following section as Carboniferous: 



Feet. 

 Limestone (youngest Carboniferous) 200 



Shales, sandstones, and conglomerates, with a basal member of chert conglomerate 1,600 



Probable unconformity by erosion. 



Thin-bedded limestone and shale, containing Carboniferous fossils 1,000 



Black shale, classed as upper Devonian but comprising the transition to Carboniferous 1,300 



The Carboniferous strata are said to embrace about 2,800 feet of sediment, 

 usually not associated with contemporaneous igneous rocks and thus distinguished 

 from the Devonian. 



Details of the sections on Porcupine River are given by Kindle,*^^ who 

 quotes determinations of faunas by Girty and floras by White. They conclude 



a Collections made by A. J. Collier. 



» Collections made by A. J. Collier and E. M. Kindle. 



c Collections made by E. M. Kindle. 



d Collections made by "W. C. Mendenhall, F. L. Hess, E. U. Kindle, and P. S. Smith. 



