PAPERS ON GEOLOGY 277 
micas, etc. The iron is still largely in the ferrous state, and the 
alkalis and alkaline earths are still present in large quantities. 
Furthermore, most of the surface of Alaska is covered either 
with forest or that thick mossy carpet, the “tundra.” Swamps 
are abundant, and in many parts of Alaska the entire surface, 
even on considerable slopes, seems to be merely one vast satur- 
ated sponge of moss and lichens grading down into black muck. 
lf buried without disturbance, this material, which decays but 
slowly, would doubtless produce coaly layers, but a large part 
of the muck is washed out by the streams and redistributed 
among the sands and silts, thus forming black or gray carbon- 
aceous sediments full of shreds of wood and fiber. The satur- 
ated and, in large part frozen, condition of most Alaskan de- 
posits effectually prevents that aeration which is requisite for 
the complete oxidation of the iron-bearing constituents. The 
red and brown colors, which such deposits often take on in 
other countries, are, therefore, seldom seen in Alaska. 
In brief, the modern terrestrial sediments of the territory, 
are typically gray or black in color, are rich in unaltered com- 
plex silicate minerals and carbonaceous matter, and are as- 
sociated locally with either coal or glacial till. They contain no 
red, and but little brown, material, no saline deposits, no 
aluminous clays, and probably not even pure quartz sands. The 
marine deposits are similar in many respects but differ in 
others. They are not yet so well known. 
Looking back over the geologic column of the upper Yukon 
Valley, and passing over the Pleistocene sediments, which we 
should readily presume were made under a climate no milder 
than the present, we first come to the Kenai (upper Eocene) 
formation in which black and gray shales and graywackes al- 
'ternate with occasional beds of coal, and contain fossil leaves 
of the poplar, birch, sequoia and oak. These all suggest a moist 
temperate climate. 
The next oldest formation of the district is the Upper Cre- 
taceous, which here consists of dark grey or black carbonaceous 
shales varying through silt-rocks to complex blackish gray- 
wacke and conglomerate. In the coarser beds of this forma- 
tion many fresh silicate minerals are visible under the micro- 
scope, testifving to the absence of effective chemical decompo- 
