418 



University of California Publications. 



[Geology 



stands at 600 feet ; and in the vicinity of Port Clarence it sinks 

 to 200 feet. 14 The uplift of the terrace was, therefore, accom- 

 panied by a considerable amount of warping, with the maximum 

 deformation along the axis of the York Mountains. The streams 

 flowing into Bering Sea have entrenched themselves in sharp 

 canyons across the bench, and this topographic evidence affords 

 the only clue to the age of the terrace. Locally some minor 

 benches but a few feet above the sea-level can be noted, and 

 testify that the general movement of uplift is still in progress. 



Inspection of the topographic map is sufficient to show that 

 the coastal plain bordering the Arctic Ocean between Cape 

 Prince of Wales and Cape Espenberg is a region of depression. 

 The York Plateau, which is broken off on its southern margin 

 by sea cliffs overlooking Bering Sea, slopes gently northward 

 to the Arctic Ocean and is buried under the Pleistocene alluvium. 

 At Shishmaref Inlet, a large, shallow embayment from the Polar 

 Sea, the lower courses of the streams are affected by tidal ebb 

 and flow, and prove the recent submergence of the region. 



The complex oscillations of the strand-line in the vicinity 

 of Nome during the late Tertiary and Quaternary time have 

 been revealed in unusual fullness of detail by the exploitation 

 of the ancient auriferous beaches. 15 Five such beaches buried 

 under the tundra of the coastal plain at depths ranging from 

 five to one hundred feet have been discovered, the youngest of 

 which is 78 feet above sea-level, and the oldest 34 feet below 

 sea-level. Fossils are plentiful in the beach deposits, which 

 consist of loose sands and gravels. Those from the beach stand- 

 ing at 78 feet above sea-level have been determined by W. H. 

 Dall to be of Pliocene age and to indicate that warmer water 

 conditions prevailed than obtain now in adjacent portions of 

 Bering Sea. 10 According to the same authority, the fossils from 

 the beach 34 feet below sea-level are of Upper Miocene or Plio- 

 cene age. 17 The geologic history as deciphered from the beaches 



14 Data based partly upon Collier 's and partly upon the writer 's 

 observations. 



is Smith, P. S., Bull. U. S. Geol. Survey No. 379, pp. 277-279. 

 ic Am. Journ. Sci., 1907, vol. 23, p. 457. 



17 Unpublished information. Cf. Journ. Geol., 1909, p. 498. 



