E. Blackic elder — Yakutat Coastal Plain of Alaska. 465 



ments of swamps and estuaries, leaves of ferns and other plants 

 find lodgment and are doubtless being preserved. Animal re- 

 mains, on the other hand, are rarer. Bones of salmon are buried 

 in the river sediments in some quantity, for millions of them die 

 each year on the spawning grounds; but, since they frequent 

 chiefly the gravelly bottoms, their opportunities for preserva- 

 tion are not the best. Land mammals are too scarce on the 

 plain to leave many skeletons. It thus appears that fossils 

 must be tolerably rare in the entire series of beds. In the 

 marine portion plants would be deficient, while mollusks, crus- 

 taceans, worms and echinoderms would predominate. In the 

 terrestrial part, bits of wood and even leaves would be locally 

 abundant, but animal remains would be rare and comprise 

 little bnt the fishes. 



The characteristics of the sediments in the Yakutat plain 

 may be summarized as follows : 



1. Origin : partly terrestrial and partly marine, the phases either 



interleaved near the contact or the one transgressing upon 

 the other. 



2. Types of sediments : till, gravel, sand, silt, mud, and peat. 



3. Composition : heterogeneous. 



4. Color : gray to black, due to the lack of oxidation products 



and the abundance of carbonaceous matter. 



5. Texture : subangular as well as round particles, alternately 



finer and coarser. 



6. Assortment : very imperfect except in the marine phase. 



Fragments of many rocks of many sizes intermingled con- 

 fusedly. 



7. Stratification : complex and irregular in the terrestrial phases. 



Cross-bedding, lense-structure and ripple-marks prevalent in 

 the sandy beds. Effects of contemporaneous erosion com- 

 mon. Sun-cracks rare. 



8. Fossils : in the terrestrial portion leaves and wood common, 



animals rare (chiefly fishes). In the marine portion shells 

 fairly common, plants rare. 



Although my subject is the modern sediments of the plain, 

 I may call attention here to the interesting fact that these sedi- 

 ments have analogs in the hard rocks of the mountains behind 

 them. The Brabazon range and the Puget peninsula are 

 composed largely of the Yakutat series,* which has been refer- 

 red to both the Carboniferous and the Jurassic systems. This 

 formation presents clearly many, although not all, of the charac- 

 teristics of the sediments in the plain just described. The 

 rocks are black slates, dark graywackes and conglomerates. 



* The lithology of the beds is desr-vibed in many papers, among them the 

 following: Harriman Alaska Exped. Report, iv, pp. 44-56 ; I. C. Russell, Nat. 

 Geogr. Mag., iii, 166-170; U. S. Grant, U. S. Geol. Surv. Bull. 284, p. 

 79-80 (Orca series). 



