78 ORIGIN ?OF LIFE IN AMEEICA 



fossil ivory might be gathered on the shores of Alaska. 

 Several Kussian 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. 



