EXPLORATION IN ALASKA IN IOX)/ GILMORE 



21 



Upon ascending to the top of the escarpment at the point most 

 remote from the river, it was found that a mass of frozen muck, 

 estimated to be two hundred feet long and fifteen to twenty feet in 

 thickness, with a vertical face of twenty to thirty feet, had moved 

 outward at its, center for fully fifty feet, but had not yet become 

 detached at its ends. The crevasse formed by this displacement was 

 filled by water to such a depth that the bottom could not be found 

 with a long pole. Back of the crevasse, in the surface of the bluff. 

 were numerous parallel cracks varying from six to eighteen inches 

 in width and many feet in length. These had water standing in 

 them nearly to the top of the ground. The conditions observed 

 here appeared to the writer to explain the presence of the ice on the 



Fig. 3. — Cross-section of "Palisades"' Escarpment, showing Formation of 



Superficial Ice. 



1-2-3. Blocks of frozen silt ; 4-5. Water level of the Yukon ; 4-6. 150-170 

 feet; 7. Crevasse filled with water; 8. Ice on faces; 9. Overhanging turf; 

 10. Lacustrian silts; n. Detritus (thawed muck). 



faces below. With the advent of winter, assisted by the already 

 frozen ground, the water in the crevasses becomes frozen solid. A 

 subsequent outward movement of the blocks would leave the ice 

 clinging to the face of either the cliff, or the block, or both, and 

 under the influence of the rays of the summer sun would rapidly 

 smooth the broken and ragged edges. On the faces of blocks I and 

 2 (see fig. 3) such layers of ice were observed, and where protected 

 by the wet mantle of overhanging turf and moss were thawing very 

 slowly. In places the ice was so thin the writer with a few strokes 

 of his pick was able to penetrate it and into the frozen muck wall 

 behind. Sections of the ice, protected by curtains of turf and falling 

 debris, would persist for considerable periods. In places it had 

 melted away, leaving its mould in the face of the cliff. 



