LOWER CEETACEOUS. 



635 



The fossils identified by Whiteaves from the Tutshi series of McConnell com- 

 prise: 



Trigonia, small, arcuate, and beaked species. Two other Pelecypoda, imperfect and 

 undetermined. Shales with numerous valves of an Estheria or of very young specimens of 

 Inoceramus. Also two crushed fragments of a small ammonite, apparently referable to Pri- 

 onocyclus woolgari. These are all placed under the head "Cretaceous" and are probably 

 lower Cretaceous as described above. 



Stanton's comment" on the above identifications is that the only specific 

 name mentioned is characteristic of the Upper Cretaceous. 



Q 4-5. KOYTIKTrK BASIN, ALASKA. 



The Koyukuk "series" is a Lower Cretaceous or possibly Jurassic terrane, 

 consisting of impure limestone, slate, and some sandstone, associated with igneous 

 rocks. It carries Aucella crassicolUs Keyserling. It occupies a large area in the 

 lower Koyukuk basin, where it was first distinguished by Schrader.^"" 



Q 7. UPPER YUKON, ALASKA. 



The latest report on the upper Yukon, that of Brooks and Kindle,'"^ gives the 

 following section of the later Mesozoic rocks (post-Triassic) : 



Provisional stratigrapJiic table. 



System. 



Series. 



Lithologic character. 



Locality. 



Upper Cretaceoua. 



Cretaceous. 



Lower Cretaceous or Up- 

 per Jurassic. 



Conglomerates, sandstone, slate, and 



shale, cut by granite. Invertebrate 



fossils. 



Unconformity. 



Siliceous slate and quartzites, with some 



tuff and a little limestone, cut by basic 



dikes. Invertebrate fossils. 

 Unconformity. 



Wolverine Mountains, Quail 

 Creek, near Rampart. 



Upper Yukon River, between 

 Fourth of July and Coal 

 creeks. 



The only member of the Mesozoic extensively developed along the Yukon is the so-called 

 Aucella beds, which may be either Jurassic or Lower Cretaceous, but may here for convenience 

 be assigned to the latter system. These Lower Cretaceous beds form a practically continuous 

 belt along the Yukon from about the mouth of Fourth of July Creek to Coal Creek. There may 

 be, however, some of the younger Tertiary beds included within this area which were overlooked' 

 in the hasty examination. 



The Lower Cretaceous of the upper Yukon comprises a series of closely folded rocks char- 

 acterized by a large amount of silica. They included primarily siliceous slates, slaty sandstones, 

 and quartzites, with which are associated some argillites and pyroclastics. One heavy bed 

 (50 to 70 feet thick) of massive tufaceous conglomerate was observed within the Mesozoic area 

 about 5 miles below Washington Creek, but may be an infolded older or younger terrane. The 

 pebbles of this conglomerate, which are chiefly hmestone, are weU rounded, and some 

 are 2 feet in diameter. The dominating rock type of the Lower Cretaceous is a siliceous slate 

 or quartzite, sometimes interbedded with a clay slate. These rocks are usually pyritiferous 

 and iron stained when weathered. Three miles below Washington Creek there is a series of 

 beautifully banded slates and quartzites. * * * 



These rocks in a general way strike easterly and northeasterly, but there are many local 

 variations. They are usually closely folded, and no deternaination of thickness, which probably 

 does not exceed a few thousand feet, could be made. On Washington Creek they appear to 

 rest unconformably on the Devonian and in turn are unconformably overlain by the Tertiary 



a Personal communication. 



