462 E. BlacJcwelder — Yakutat Coastal Plain of Alaska. 



particles of slate, greenstone, quartz, feldspar and ferromag- 

 nesian minerals, with a varying admixture of carbonaceous 

 material. A lack of the usual products of oxidation is the 

 striking characteristic of all the deposits. 



In general the sediments do not show evidence of long con- 

 tinued attrition. Although the pebbles and sand grains are 

 moderately round, many particles are angular or irregular in 



Fig. 2. 



Fig. 2. The delta of the Alsek River as seen from the Brabazon Range on 

 the north. A type of the constructing rivers of the foreland (photograph 

 by Netland, U. 8. Boundary Survey). 



shape. The assortment and segregation of the particles, both 

 as to size and lithologic character, is also markedly imperfect. 

 The gravels are heterogeneous mixtures of bits of slate, gray- 

 wacke, granite and other rocks. The sands contain feldspar, 

 magnetite, hornblende and slate in addition to the usual quartz. 

 In the matter of size also the same lack of assortment pre- 

 vails, large pebbles and small being bound together by a matrix 

 of muddy sand ; while the silty beds contain much sand and 

 mica. Heterogeneity is therefore another distinguishing prop- 

 erty of these sediments. 



Upon the surface, the distribution of the various deposits 

 is determined by their origin. At the mouths of the largest 

 valleys there are glacial moraines. Along the more powerful 

 streams there are sheets of bare gravel and mixed sands. In 

 the swampy intervening areas peaty material is accumulating, 

 Along the ocean beach, exposed to the storm waves and high 

 winds, pure quartz-sands are being heaped into low dunes ; 

 while in the tidal lagoons and estuaries just back of the shore, 



