REMINISCENCES OF YUKON EXPLORATION 129 



flowed in much their present channels. At times their flood was 

 mighty, comparable only with such streams as Amazon and Nilus. 

 Once its waters reflected the foliage of oak and plane-tree; the fig and 

 the tulip tree flourished on its banks and the heights beyond were dark 

 with forests of Sequoia. Later, its soft alluvial flats trembled under 

 the ponderous tread of the hairy mammoth, while the wild horse grazed 

 upon its verdant savannas. The bison knew its prairieland and the 

 mazama its foothills. With the wane of the Age of Ice the musk-ox 

 sought pasturage upon the Yukon tundra. 



Strangely enough, during the height of the great Ice Age when the 

 northeastern part of the continent as well as southern Alaska were 

 buried deep under a continental ice-sheet, the greater part of the 

 Yukon basin remained open to the sun. The traces of the glaciers are 

 plain to see, about its head waters, on the Alaskan mountains to the 

 south and the Yukon mountains to the north, but the terminal moraines 

 are there to show where the deadly creeping of the ice was stayed, far 

 above the present valley. During this time, perhaps, the muddy tor- 

 rents bore to the river and the sea the alluvium which now composes the 

 vast delta of the Yukon and the submarine flats, covering thousands of 

 square miles, which are the characteristic feature of the eastern half of 

 Bering Sea. With the shrinking of the glacier-sheet vast floods of 

 water were let loose upon the alluvium of the lowlands, gradually 

 shaping the features of the valley, concentrating the metallic contents 

 of the gravels, and hurrying seaward the ' mountain meal ' or im- 

 palpable white silt of the glacial grist. 



From the volcanic craters of the mountain ranges to the south and 

 west fine white ashes on one occasion poured in such volume as to cover 

 the ground with a fleecy blanket, several feet thick, for many hundred 

 square miles. Though covered by later accretions, this continuous layer 

 of white ashes may still be traced for many leagues along the steep 

 bluffs of the right bank of the river where it is under-cut by the current. 



As the glaciers receded, the water supply became less profuse, the 

 river settled between its banks, while the flats and prairies were invaded 

 by willow and poplar, birch and spruce. The flora of the north, delicate 

 and abundant, spread over the land, followed by the bee and the butter- 

 fly. Singing birds found nesting places, and with them all the small 

 wild things which populate the wilderness, to gather sustenance from 

 seed or berry, or seek refuge from the fox or hawk. And so at last the 

 valley lay complete as first we knew it. 



A brave domain, well defended, stretching some two thousand miles. 

 On the north broad tundras hardly divided by low hills from the in- 

 violate Arctic floes where they push upon the low sandy coast. To the 

 northwest a turmoil of mountains, with hardly any game, kept off the 

 explorer; while to the west, before the flatlands of the delta, lay many 



vol. lxix. — 9 



