274 WALKS AND TALKS. 



Madison. Still others streamed from Keweenaw Point and 

 Duluth into central Wisconsin and Minnesota. Wherever 

 these local ice-streams terminated, they left moraines to mark 

 the extent of their advance. This was the "second glacial 

 period." The entire continent north of an irregular line pass- 

 ing through New York, Fort Wayne, Madison, Minneapolis, 

 and Yankton, lay, like the soil of Greenland in our time, 

 buried beneath a bed of ice and snow some thousands of feet 

 thick. The summits of the Adirondacks, the Catskills, and 

 the White Mountains barely emerged above the desolate, 

 featureless waste. What went on how the subglacial ine- 

 qualities of surface strained the semi-rigid ice-stream into con- 

 formity; how the deep ice-mass snapped with loud detonations, 

 into yawning crevasses; how the summer sun gave origin to 

 superglacial streams which sooner or later lost themselves in 

 the fissures, and joined the roaring streams beneath the ice, 

 which escaped at intervals along the southern border ; how 

 they were augmented by the enormous thawing of the under 

 surface of the glacier; how these streams assorted and trans- 

 ported the subglacial debris all these things are of too great 

 interest to fail of mention, but of too great importance to admit 

 of adequate discussion. 



During this reign of ice, the snows fell which overtook the 

 long-haired elephant of Siberia and Alaska (Talk XXVII), 

 and buried them in herds. They had been browsing for 

 many generations on that northern slope. I know not to how 

 severe a climate their natures fitted them ; but clearly it had 

 not been a climate which brought perpetual snow. Now they 

 experienced a new chill in the atmosphere. Now the snows 

 descended and they crowded themselves together in ravines 

 for warmth and mutual protection. Their instincts taught 

 them this mode of self-preservation. They had often outlived 

 a snow-burial during winters preceding. But their last burial 

 finally arrived. Now no thaw succeeded the overwhelming 

 storm. No spring-time returned to release them from their 

 chilly retreat. Spring only turned the snowy blanket to ice. 

 Other winters buried the mammoth beneath added beds of ice. 



