GENERAL GEOLOGY 393 



islands and the Alaska peninsula, having their eastern termination on 

 cape Douglas, at the mouth of Cook inlet. The Kenai mountains occupy 

 the southeastern half of the peninsula of that name, and have their west- 

 ern termination - at cape Elizabeth, with a possible detached extension 

 in the lower summits of Afognak and Kodiak islands. 



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 Meso- 

 zoic 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 inlet 

 has its general position outlined by a number of great overthrusts, b}' 

 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 cross-cut by an irregular series of faults. 



The general distribution of the Mesozoic rocks throughout the region 

 discussed is shown in the sketch map, figure 1, and a somewhat more 

 detailed map of part of the coast of Cook inlet is given in figure 2. 



Mesozoic Formations and Faunas 

 upper triassic 



Upper Triassic rocks have been seen on the north shore of Bear cove 

 and on Bear bay, both on the west shore of Cook inlet, and on the Alaska 

 peninsula at the entrance to Cold bay and extending several miles east- 

 ward. They are also probably present at numerous localities on the 

 south shore of Kachemak bay, as at Halibut cove and Seldovia. where 

 there is a great development of thin bedded and contorted cherts, with 

 some silicious limestone and igneous rocks. This series is tentatively 

 correlated with the fossiliferous Trias on the west shore of Cook inlet on 

 account of lithologic and structural resemblances and because of its 

 association with the Lower Jurassic. 



The Triassic rocks of Cold bay, Bear cove, and Bear bay, whose age 

 has been definitely determined by fossils, consist of thin bedded chert, 

 limestone, and shale of varied colors. The chert and limestone are 

 usually dark-black, green, or dark-red when fresh, but weather to lighter 

 shades. No measurement of the thickness has been made, but it is esti- 

 mated to be at least 2,000 feet in the exposures seen by us, in which the 

 base was always cut off by intruded igneous rocks. 



These rocks are always closely folded and are frequently crumpled. 

 They are usually cut by numerous dikes of diverse character and com- 



