lit', i.i. |;|'--l I I 1 I ; I \ < I (iEOLOCrt OF ALASKA. 



\ nong the Dumeroua problems awaiting examination by observant trav- 



rs in Alaska is the determination ol the i stent and source <>!' this deposit. 



/• ■ / Th( level-topped bluff known as the" Palisades," below 



the mouth of the Tan an ah, has already been mentioned. The Btrata forming 

 these bluffs ha i y appearance of being lacustral b< diments. The erosion 



a Bt ream channel across the level plain formed by the bottom of the old 

 lake has lefl portions of it in the form of a broad terrace, bounded on one 

 side by th< river bank and <>n the opposite Bide by encircling hills. 



This terrace appears level, but it is nol a lake terrace as thai term is usually 



underel 1. neither i< it a stream terrace ; for convenience it may be termed 



& plateau \\ the mouth of Pelly river a broad, nearly level lava 



coulee has been cut by the Yukon and by the Pelly, and forms another 

 example of this kind of terrace. 



'I'h.' I., wea between lakes Lebarge anil Marsh has excavated a deep 

 channel across a plain formed of the sediment of a post-glacial lake, described 

 below under the name of Lake Yukon, ami has hit a broad level area on 

 each Bide of its c turse Bimilar in every way t" the terrace of older date at 

 the Palisadi 



Examples of plateau terraces air < imon in many other regions, ami the 



nam.- here proposed may he found sufficiently convenient for adoption by 

 ;_''■"! graphers who study the origin of topographic forms. 



hah Terraces. — Horizontal terraces occur all about the borders of the 

 lakes drained by the I . -.at various elevations up to Beveral hundred feet. 

 These water lines were formed by an ancient lake which has m,w passed 

 away: or perhaps more correctly, has been drained sufficiently to become 

 divided into a number of independent water bodies, of which lakes Lebargi . 

 Marsh, Tagish, and Bennett arc the best -known exainplt 



A- the ancient lake hd-c referred to will doubtless receive attention in the 



future. I have proposed to name it after the river which drained it. 



I. \k i Yukon. 



/'■ ervatione. — Numerous observations concerning the terraces 



and sediments <>f Lake Yukon may !»• found in Dawson's report of a recon- 

 nou a tie Yukon district. The terraces were also noticed bySchwatka 



while descending the Lew,- in 1883.1 



/' m and Extent. The first evidence of the former existence of an an- 

 "ii the head-waters of the Yukon which one meets in ascending 



that ri in the neighbor! I of the mouth of Little Salmon river. 



Thence up to the mouth of the Lew,-, and up the Lew,- to Lake 



p in. 



