UPPER JURASSIC 403 



" The Naknek series consists of a great thickness of granitic arkose and of con- 

 glomerate which generally contain pebbles of granite. All of these sedimentary 

 rocks are evidently derived from the destruction of a land mass which consisted 

 largely of hornblende-biotite-granite. There are probably some volcanic flows 

 interstratified with the arkose and conglomerates, although it is not absolutely 

 proved that those examined may not be intrusive. The series is cut by andesite- 

 basaltic (aleutitic) lava of later age, especially along the axis of the range, where 

 the amount of volcanic rock is very great. 



" Throughout the whole series the arkoses carry abundant fossil remains, both 

 of plants and of marine organisms." 



Elsewhere he alludes to the presence of beds of gray compact lime- 

 stone in the formation, and on page 180 he adds : 



" Throughout the whole series are abundant plant remains, which, so far as 

 examined, were not determinate, and marine faunal remains that indicate a prob- 

 able Upper Jurassic age." 



He estimates the thickness exposed in the mountains near Katmai as 

 at least 1,500 feet. The section in the cliffs on the east side of Katmai 

 bay is described as consisting of hard and massive dark-gray granite 

 arkose at the bottom, overlain by a probable flow of massive andesite, 

 above which are arkose and conglomerates. Gray compact limestone 

 with Jurassic fossils is found at various points in the rocks. 



The Naknek formation occupies a large area on the Alaska peninsula, 

 in the vicinity of Katmai and Naknek lake, extending southward beyond 

 Cold bay and Becharof lake. It also extends along the shore of Cook 

 inlet from Snug harbor to the mouth of Enochkin bay and occurs on 

 the shore of Kamishak bay between Bear cove and Bear bay, south of 

 Bear bay and west of Douglas river. Wherever its base is seen it rests 

 conformably on the Enochkin formation. 



The following sections show the development of the formation in 

 exposures on the west shore of Cook inlet : 



Section of Naknek formation on the north shore of Chinitna bay 



Feet 



Tertiary shales, sandstones, and conglomerates with a few Kenai plants 



Coarse conglomerate with 6-inch (maximum) granite pebbles and smaller 



pebbles of various lithologic character in a tuffaceous or arkose matrix. . . 10 



Shaly arkose or sandstone 2\ 



Conglomerate 2\ 



Arkosic sandstone or andesite 1| 



Conglomerate 1 



Massive tuffaceous rock with numerous inclusions , 9 



Tuffaceous rock with much shale 3 



Andesite. 12 



Shale 2 



Concealed 10 



