688 G. C. MARTIN TRIASSIC ROCKS OF ALASKA 



Alaska, as in the Alps, in the Himalayas, and in the western part of the 

 United States and of Canada it is generally, if not invariably, restricted 

 to mountain regions of the Alpine (structural) type. The general world- 

 wide geographic accordance of the present areas of marine Triassic rocks 

 with mountains of Alpine form, structure, and date has previously been 

 recognized, and has been stated by Freeh* as follows : 



"Scarcely in any period of the earth's history is the connection between the 

 distribution of mountain zones and later sedimentation so clearly expressed as 

 in the Trias. 



"1. The provinces of the late Taleozoic folding correspond to tbe continental 

 development of the Trias. 



"2. The great Mediterranean sea of Eurasia and the margin of the Pacific 

 Trias-ocean coincide with the zones of the Tertiary high mountains. Only the 

 eastern margin of the Cordilleras (that is, the Rocky Mountains of North 

 America, in a strict sense) contain a continental development of the Trias. 



"3. The flat-lying Arctic Trias ( Spitsbergen, North Siberia, Arctic (extra- 

 Pacific) North America), where neither late Paleozoic nor Tertiary mountain 

 building is encountered, can not be regarded as an exception to the above rule, 

 but belongs, in a tectonic sense, to an indifferent province.'' 



"The dependence of the distribution of the oceanic Trias on the later Al- 

 pine — that is to say, Eurasian and circumpacific — folding has been repeatedly 

 emphasized, and means essentially that the accumulation of thick masses of 

 sediments in the geosynclines determines the later folding. From northern 

 Spain, the Balearies, Sicily, the Alps, and Dinarics to the Himalayas and Su- 

 matra the same uniform law holds that also governs on the circumference of 

 the Pacific Ocean. Here we see, also, from Alaska, Kamchatka, and Japan to 

 New Caledonia. New Zealand, California, Mexico, Colombia, and Peru, the 

 oceanic Trias constantly appearing in the provinces of Tertiary mountain build- 

 ing, which, without exception, are coincident with a great thickness of sedi- 

 ments." 



The Alaskan instance is noteworthy not only because it is an additional 

 example, lint because the law holds there in such remarkable detail. 



All the Triassic rocks of Alaska that are now known belong in tbe 

 Upper Triassic, except for a single Middle Triassic occurrence on Seward 

 Peninsula, It is probable that the Lower Triassic and much of the Mid- 

 dle Triassic are not represented in the Alaska rocks, except possibly by 

 terrestrial volcanic rocks or by some metamorphosed strata of very doubt- 

 ful age. 



CHARACTER OF THE PRE-TRIASSIC BASEMENT 



In general. — Before proceeding with the description and discussion of 

 the known Triassic rocks of Alaska, it is important that we consider the 

 character of the basement on which these beds were laid down. 



4 Fritz Freeh : Kiickblick anf die Trias. Lethcea geognostica, Teil II, Bd. 1, Lieferung 

 4, 1908, pp. 510, 518. 



