PAPERS ON GEOLOGY 279 
tion with the typical black and gray slates, graywackes, and 
limestones. Even in rocks which are believed to be of pre- 
Cambrian age, similar types persist; for the dark schistose 
craywackes, slates and chlorite schists contain much undecayed 
feldspar and ferromagnesian constituents darkened with a fine 
graphitic dust. 
In order to see how districts outside of those with which I 
was personally familiar compared in this respect, I examined 
the stratigraphic sections in the geological reports on seven 
districts well distributed over the territory.. Out of some 
twenty-two different formations described, there were four 
which differ from the typical Alaskan group of sediments. 
These were white limestone, buff sandstone, gray limestone, 
and red and green cherts. All the other formations consisted 
of black or dark gray carbonaceous shales, dark colored ar- 
koses, graywackes, graywacke conglomerates, undecayed pyro- 
clastics, tillites, etc. If the examination had been continued 
to include all of the Alaskan districts which have been studied 
in some detail, the results would not have been very different. 
This seems to show clearly that there is not only a character- 
istic modern type of Alaskan sediments, but that in earlier 
periods, back even to the pre-Cambrian, this type predominated, 
Carbonaceous shales, silt-rocks, and graywackes are char- 
acteristic, instead of the purer sandstones and clay shales of 
eastern United States. 
As a corollary, it is significant that throughout Alaska there 
is an absence or rarity of certain types of sedimentary rocks, 
Among: these are the saline deposits characteristic of desert 
regions, the red bed facies now generally ascribed to the in- 
fluence of hot climates with alternating seasons, as well as the 
pure white limestones, coral reef rocks, and oolites, which are 
today forming in tropical seas, 
In short, the combined evidence strongly suggests that the 
cool, moist climate of modern Alaska—oscillating now and 
then toward the glacial Arctic condition on the one hand and 
toward the moist temperate on the other—has been persistent, 
with but few real interruptions, throughout the known ge- 
ologic history of Alaska. If this proves to be a sound con- 
