78 
ORIGIN l OF LIFE IN AMERICA 
fossil ivory might be gathered on the shores of Alaska. 
Several Russian authorities reported on its occurrence there, 
animadverting to the fact that the remains of elephants had 
also been discovered on some of the Pribilof Islands. Within 
recent years several expeditions have been sent to Alaska 
from the United States with a view to discovering more about 
these and other remains of extinct animals. The first of these 
was dispatched by the Smithsonian Institution of Washington 
in 1904. Mr. Maddren, who had already visited the country 
several times and had travelled extensively in the interior, 
was charged with the expedition, and he issued an interesting 
report on his return. 
He contends that the lowest beds in Alaska in which 
mammoth remains occur are the “ lacustrine silts,” which 
form an extensively developed feature in the country. 
Scattered through these Pleistocene deposits we find remains 
of skeletons, isolated cheek-teeth, tusks and bones, the animals' 
to which they belonged having probably died near the shores 
of the lakes in the bottom of which they became embedded. 
These fluvial and lacustrine beds of Alaska, with their occa¬ 
sional gravels, rest unconformably on the eroded surfaces 
of the older formations. At the time the silts and clays were 
forming Alaska was for the most part, according to Mr. 
Maddren,* a low-lying country, characterised by enlarged 
rivers with slow drainage, and many lakes. 
The general conclusions arrived at by Mr. Maddren are, 
“ that while remnants of the large Pleistocene mammal herds 
may have survived down to the recent period, and in some 
cases their direct descendants, such as the musk ox, have 
done so, most of them became extinct in Alaska with the close 
of the Pleistocene. The most rational way of explaining this 
extinction of animal life, says Mr. Maddren, is by a gradual 
alteration of the climate from more temperate conditions, per¬ 
mitting of a forest vegetation much further north than now, 
to the more severe climate of to-day. Recent changes, while 
checking the vegetation and thus reducing the food supply, 
have acted injuriously on animal life, only leaving those 
forms that were capable of adapting themselves to the new 
* Maddren, A. G., “ Smithsonian Exploration in Alaska,” pp. 25—28. 
