EAELIER TERTIARY (EOCENE AND OLIGOCENE). 



783 



N 4, O 4-5. ALASKA PENINSULA. 



The general geology of the Alaska Peninsula was thus stated by Stanton and 

 Martin :^«^ 



The Alaska Peninsula contains a coarse crystalline core of granite or of similar rocks, flanked 

 on the eastern side by Mesozoic sediments and on the western side by late Tertiary or post- 

 Tertiary beds. The Mesozoic beds are overlain in places by early Tertiary formations. Both 

 the Mesozoic and the Tertiary beds are cut by andesite and basalt. The intrusion and volcanic 

 outflow has continued from late Jurassic time until the present, the region containing several 

 active volcanoes. 



The structure of the region is varied. The west shore of Cook Inl^ has its general position 

 outlined by a number of great overthrusts, by which the Triassic rocks have been brought in 

 contact with the Upper Jurassic. The Alaska Peninsula is a region of open folding, with the 

 folds crosscut by an irregular series of faults. 



At Herendeen Bay Atwood/^"^ in 1908, distinguished the following section: 



Geologic sequence in western fart of AlasTca Peninsula. 



Atwood's comment follows: 



Eocene, Miocene, and post-Miocene formations are exposed m this portion of the penin- 

 sula. The Eocene strata include at least 5,000 feet of sandstone, shales, conglomerates, and 

 seams of lignite and form the central portion of the Aleutian Range in the Balboa-Herendeen 

 Bay district. They extend westward at least as far as Pavlof Bay and eastward to the Chignik 

 Bay region. Several collections of fossil shells and plants have been procured from these beds. 

 The shells are those of marine invertebrates and have been determined by W. H. DaU to be of 

 upper Eocene age. Mr. Dall reports that some of the material from these strata may be upper 

 Eocene or Oligocene. The plants, as determined by F. H. KJnowlton, are all of Kenai age. 

 They were procured from beds that are interstratified with those from which the shells were 



