(JharacterislicH of OrevaHfies. 181 



l)l<)\vii froni ]]('A'^]\]}(}r\\)ir cWiYs. It in jilniost (^ntircily free froiu 

 moni'mcH, hut at tlio hjiHOH of ,stc(.-]j k1()[jch Hrnull ureaH of (]('briH 

 Hoii)f(tiiu(!S a))p(;ar at the surfafo wIkmi the y(!arly molting has 

 ]'(!ach(!(l its iiiiixiiiiuui. T\\('. ahsonf',(3 of moraines is acf-oiiipanicid 

 hy an al>seiK',e of j^hieial tahh^s, san(l-(;ones and other details of 

 glacial surfaces due to differential melting. Streams S(;ldom 

 api)ear at the surface, for tin; r(;ason that usually the water ]>ro- 

 dueed by surface melting is quickly absorbed l^y th(; jjorous 

 strata l)eneath ; yet the crevasses are frefjuently filled with water, 

 and sometimes shallow lakes of deep blue occur at the bottc^ms 

 of the amphitheatres and form a marked contrast- to the even 

 white of the general surface. Crevasses are present or absent 

 according to the slope of the surface on which the neve rests. 

 In. the crevasses the edges of horizontal layers of granular ice 

 are exhibited, showing that the neve down to a depth of at least 

 one or two hundred feet is horizontally stratified. In the St. 

 Elias region the strata are most frequently fr«)m ten to fifteen 

 feet thick, but in a f(;w instances layers without partings over 

 fifty feet thick were seen. The surface is always of white, gran- 

 ular ice, but in the crevasses the layers near the bottom appear 

 more compact and bluer in color than those near the surface. 



Some of the most striking features of the neve are due to the 

 crevasses that break their surfaces. The orderly arrangement of 

 marginal crevasses and of tlie interior crevasses at the rapids in 

 the Seward glacier have already been referred to; but there 

 are still other crevasses, especially in the broad, gently sloping 

 portions of tlic; snow-fields wdiere the motion is slight, which, 

 although less regular in their arrangement, are fully as interest- 

 ing. The crevasses on such slopes generally run at right angles 

 to the direction in which the snow is moving. On looking down 

 on such a surface, the breaks look like long clear-cut gashes 

 which have stretched open in the center, but taper to a sharp 

 ])oint at each end. The ability of the neve ice to stretch to a 

 limited extent is thus clearly shown. The initiation of the cre- 

 vasses seems to be due to the movement of the n6ve ice over a 

 surface in which there are inequalities of such magnitude that 

 the ice cannot stretch sufficiently to allow it to accommodate 

 itself to them, so that strains are produced which result in frac- 

 tures at right angles to the line of general movement. Crevasses 

 found where the grade is gentle vary from a fraction of an inch 

 to 10 or 15 feet in width, and are sometimes two or three thou- 



25— Nat. Gjion. Mag., vol. Ill, 1891. 



