632 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



Atwood*^* reports on the Jurassic and Cretaceous of the Alaska Peninsula as 

 follows : 



Geologic sequence in western part of Alaska Peninsula. 



The Upper Jurassic sediments are * * * dense, fine-grained sandstones of bluish 

 color, conglomerates, shales, and arkose. They are the oldest sedimentary rocks exposed in 

 either the Chignik or the Herendeen Bay districts. * * f ^\^q Chignik localities have 

 yielded several collections of invertebrate fossils whose age has been determined by Stanton. 



The Upper Jurassic beds in Pinnacle Mountain, Herendeen Bay, are overlain by Cretaceous 

 rocks and both have been folded, truncated, and in part covered by volcanic material, which 

 issued from the summit of Pinnacle Mountain. The exposures on the west shore of Herendeen 

 Bay * * * consist chiefly of fine-grained blue sandstones. [The fossils have been exam- 

 ined by Stanton], who reports that within the Upper Jurassic of Herendeen Bay two horizons are 

 represented. At the upper horizon are forms related to AuceUa faJlasi. * * * At the 

 lower horizon are forms related to AuceUa ironni. * * * 



Among the collections procured from the Chignik Bay region there are no fossils of Lower 

 Cretaceous age. In parts of this region, at least, the Upper Cretaceous beds unconformably 

 overlie the Upper Jurassic, and it may be that there is no Lower Cretaceous in the region. In the 

 Herendeen Bay district the Lower Cretaceous appears in three belts extending through the 

 Herendeen Bay coal field, coming to the surface on the flanks of the folds. The fossils * * * 

 from these formations indicate that there are two horizons within the Lower Cretaceous. At 

 the upper horizon are forms related to AuceUa crassicollis, and at the lower are forms related 

 to AuceUa piochi. * * * The sediments * * * consist of sandstones, shales, and 

 conglomerates. 



O 8. SOTJTHEASTEBN ALASKA. 



The Cretaceous rocks of southeastern Alaska comprise Aucella-bearing beds, 

 which are Lower Cretaceous or possibly Jurassic, and a higher terrane, apparently 

 unconformable to the Aucella-bearing beds, but conformable to the overlying Kenai 

 formation (Eocene) and containing plant remains. Brooks ^''" thus sums up the 

 known facts: 



The recent studies of Wright have revealed the presence of the AuceUa-bearing beds along 

 the eastern coast of Admiralty Island in a series of conglomerates, graywackes, and slates. 

 Stanton makes the following statement in regard, to the fossils from these beds: 



"The specimens of AuceUa from Pybus Bay, Admiralty Island, are apparently referable to 

 species that in California and adjacent States are characteristic of the Lower Cretaceous, 

 AuceUa piochii occurring in a lower zone than AuceUa crassicollis. The Alaskan specimens prob- 

 ably also come from the Lower Cretaceous, although strict correlation is rendered somewhat 

 hazardous by the fact that the genus AuceUa with similar specific forms ranges down into the 

 upper Jurassic." 



