718 G. C. MARTIN TRIASSIC ROCKS OF ALASKA 



terbedded with strata of other kinds. The fauna of these supposed Karnic 

 beds of southern Alaska is of the Mediterranean type and probably indi- 

 cate warm-water conditions. The transgression of the Karnic sea was 

 probably from the south. Limestones that presumably were synchronous 

 with these, but which possibly were laid down in different basins that may 

 have maintained a connection with the boreal sea, are known in the pres- 

 ent sites of the Rocky and the Arctic Mountains or on the upper Yukon 

 and on the eastern part of the Arctic slope. 



The sea probably receded in Lower Noric time from the greater part 

 of Alaska, for rocks of supposed Lower Noric age are definitely known 

 only in the vicinity of Iliamna Lake, where they are represented by lime- 

 stone containing a warm- water coral-reef fauna. 



The Upper Noric was the time of a great transgression of the sea, when 

 the greater part, if not all, of Alaska was submerged. The supposed 

 Upper Noric rocks consist of shales, impure limestones, and cherts, with 

 locally some volcanic beds. They contain a boreal fauna that is allied to 

 that of northern Asia and that possibly indicates a cold-water sea in con- 

 trast with the preceding warm-water seas of Karnic and of Lower Noric 

 times. This marked difference in faunal conditions, together with the 

 general absence of Lower Noric beds between the Upper Noric and the 

 underlying Karnic strata and with the strong suggestions of an uncon- 

 formity at the base of the Upper Noric beds (see pages 695, 701, 711), 

 indicates that there was an important recession of the sea at the end of 

 Karnic time. The invading Upper Noric sea probably came in from the 

 northwest. 



There was a general emergence of the land at the end of Noric time, 

 when the sea probably retiied beyond the present continental limits. 

 Rhsetic and early Lias deposits are not known in Alaska, and it is believed 

 that the continent stood above sealevel from the end of Noric until late 

 Lias (Toarcian) time. An important period of folding followed the 

 deposition of the local Upper Triassic strata, but the date of this folding 

 has not been determined more closely than post-Triassic and pre-Upper 

 Jurassic. The beginning of the local record in Jurassic (probably Upper 

 Lias or Toarcian) time was marked by a moderate submergence, accom- 

 panied or followed by intense volcanic activity along the present Pacific 

 seaboard. 



