■^ HOBBS— CHARACTERISTICS OF THE [April 22, 



warmed surface layer to the whole fragment — (a) in a dust well, 

 {b) in a pebble that sinks slightly into the ice until it reaches equi- 

 librium, (c) in a slab of such size as to neither facilitate nor retard 

 surface melting, and (J) in a large protective slab of rock. 



The basins which result from the dust wells induce still other 

 interesting structures. At night the water within these basins freezes 

 in the form of needles which everywhere project inward from the 

 steep walls of the basin. After repeated freezings the basins are 

 often entirely closed by these needles and thus form "glacier stars " 

 (see Fig. 35, c). Elongated basins have been given the name 

 bagnoires (see Fig. 35, d). 



From studies of such phenomena resulting from differential 

 melting as developed upon the Great Aletsch glacier, we have found 

 that the segregation of the rock debris upon the bottom of the basins 

 later protects those areas after melting of the general surface has 



Fig. 2:7- Section of the so-called " cryoconite holes " upon the surface 

 of an ice hummock (after Nordenskiold). 



drained them of their water. Thus the familiar debris-covered ice 

 cones come into existence and further increase the irregularities 

 of the ice surface. The dust wells and basins which were described 

 by Nordenskiold covered over large areas the sides of steep hum- 

 mocks in the ice as well as its more level surfaces (see Fig. 2)7) ■ 



On his return from his attack upon the inland-ice near Disco 

 Bay, Peary travelled for seven hours through half-frozen morasses 

 alternating with hard blue ice honey-combed with water cavities. 

 Then the character of the ice completely changed, the slush and the 

 water cavities disappeared, and the entire surface was granular 

 snow-ice, scored in every direction with furrows, one to four feet 



