MBSozoic 307 



Lot 19. — North bank of Yukon river, (i miles above Charlie village : 



This collection contains numerous specimens of Aucella cf. crassicollis Key- 

 serling. This is provisionally referred to the Lower Cretaceous, although the 

 possibility that it may be Jurassic should not be forgotten. 



Lot 21. — South bank of the Yukon river, 1% miles below Sams creek: 



This small lot contains two imperfect specimens of Aucella and a few small 

 fragmentary imprints of luoceramus. The horizon is probably the same as 

 that of lot 19. 



The reference of these three lots of fossils provisionally to the Lower Cre- 

 taceous is made with the same reservation that has so often been expressed 

 when similar collections containing Aucella and only a few associated forms 

 have been submitted from this and other areas in Alaska — that is, while the 

 Aucella itself is indicative of probable Cretaceous age, closely related species 

 are known in the Jurassic, and it may be that all of the Aucella beds of 

 Alaska are Jurassic. 



These Aucella-bearing beds of the upper Yiikon were included by 

 Spurr^^^ in his Mission Creek series, which he provisionally assigned to 

 the Upper Cretaceous or Jurassic. As, however, he also included in his 

 Mission Creek terrains which have since proved to be either Tertiary or 

 Paleozoic, it does not appear to be advisable to perpetuate this name as a 

 stratigraphic unit. The same rocks have also been described by CoUier,^^^ 

 but he did not propose any formation name, nor does it seem desirable tc 

 do so here, in view of the paucity of the information regarding these 

 beds. Sediments of the same age are widespread in Alaska, but will not 

 be discussed here. 



In 1905 Prindle^^* and Hess reported the occurrence of a Cretaceous 

 sandstone in the Eampart region. More recently Prindle^^® has revisited 

 this locality and found fossils assigned by Doctor Stanton to the Upper 

 Cretaceous. The rock in which this fauna occurs is a black, carbonaceous, 

 sandy argillite. Granitic rocks are found cutting these beds, showing a 

 later intrusion of acid rocks than was previously known. Collier^^" found 

 Upper Cretaceous beds on the lower Yukon near Nulato, but aside from 

 these this horizon is unknown in central Alaska. 



TERTIARY 



The most widely distributed formation of the Yukon hasin is repre- 



"28 Opus cited, pp. 175-184. 



^^ Arthur .1. Collier : The coal resources of the Yukon. BuUetin no. 218, U. S. Geo- 

 logical Survey, pp. 16-17. 



'=''Ij. M. Prindle and F. L. Ile.ss : The sold phicers of the nampai-t rosio"- nullclin 

 no. 280, U. S. Geological Survey, p. 22. 



"» L. M. I'rindle : Descriptions of the Fairbanks and Rampart quadrangles. Bulletin 

 no. 337, U. S. Geological Survey. (In print.) 



!=» Bulletin no. 218, U. S. Geological Survey, pp. 15-17. 



