Summary of Conclusions 65 



dizing of peat and humus and is more often found in situations 

 where there are no traces whatever of animal remains. It is clearly 

 and solely referable to decaying vegetable matter and in no case to 

 animal matter in the Pleistocene clays. 



It appears safe to assert that even when found intimately asso- 

 ciated with mammal remains on talus slopes all occurrences of ice 

 are to be considered more as an afterthought in studying the Pleis- 

 tocene deposits of Alaska (and Siberia) with their fossil remains. 

 The phenomena of Pleistocene and Recent are confused only super- 

 ficially as is to be expected. The land ice bears no relation to the 

 mammoth and its contemporary fauna beyond that the conditions of 

 gradually increasing cold that have brought about the occurrence 

 and preservation of the ice phenomena as exhibited today in Arctic 

 and sub-Arctic regions was apparently also the primary cause of 

 the extinction of the mammoth. The mammoth has become asso- 

 ciated with ice because its remains have been found intermingled 

 with ice on talus slopes. This is to be expected in clay bluffs 

 overlain by beds of ice which in turn are covered by layers of peat 

 or alluvium. In undergoing a vertical displacement due to the 

 undermining of the sea or rivers, the ice may be fractured into large 

 blocks by uneven stresses during its descent, the peaty covering 

 become torn so fragments of it mixed with clay are washed down 

 and over the new surface to fill up the cracks between the frozen 

 blocks. Thus any mammoth or other remains that may be im- 

 bedded in the clays may become mixed heterogeneously with the 

 re-sorted material among the ice blocks or lie exposed. Thus a 

 frozen carcass may readily fall intact to find a secondary resting 

 place in a crevasse between ice blocks and there be refrigerated. 



XII. — Summary of Conclusions 



I. That while remnants of the large Pleistocene mammal herds 

 may have survived down to the Recent period and in some cases 

 their direct descendants, as the musk-ox, to the present, most of 

 them became extinct in Alaska with the close of Pleistocene. 



II. The most rational way of explaining this extinction of ani- 

 mal life is by a gradual changing of the climate from more temper- 

 ate conditions permitting of a forest vegetation much farther north 

 than now, to the more severe climate of today, which subduing the 

 vegetation and thus reducing the food supply besides directly dis- 

 comforting the animals themselves, has left only those forms 

 capable of adapting themselves to the Recent conditions surviving 

 in these regions to the present. 



