742 /. H. OGILVIE 



region; to prevent this formation, in the other. The result of this 

 method of formation is that the valley glaciers on the east are entirely 

 in the region of melting, and that the new snow supply they receive 

 has no connection with their own forward movement.^ It might 

 therefore be expected that their rate of melting would be greater than 

 that of the glaciers with great neve regions as reservoirs of accumula- 

 tion. That this is not the case seems to be due entirely to the remain- 

 ing factor of waste. 



Amount of sunlight and of air received by the ice. — There are two 

 causes which combine to shade the eastern glaciers: (i) shading by 

 the steep cliffs, and (2) covering by debris. The shading by cliffs 

 seems sufficient to determine the general position of the ice in its 

 valley. This position of equilibrium once determined, the debris 

 covering becomes the determining factor. That it is so is shown 

 by the melting of the inter-debris areas, and its effectiveness is due 

 to protection from both melting and evaporation. 



GENERAL CONCLUSIONS 



The type of glacier here described under the first group is nut a 

 common one, and probably exists only in regions of sharp relief and 

 moderate precipitation. Less relief would afford opportunity for- 

 snow-fields to accumulate; greater snowfall would fill the valley, 

 connecting the valley glacier with the cliff glaciers above, and so 

 keeping the debris subglacial throughout. Either cause would 

 produce a glacier of the second group — the ordinary type. Among 

 glaciers of this ordinary type the concentration of debris on the 

 surface at the lower end is a part of the process of retrogression, 

 representing a stage of decadence.^ The ice, if thus protected, is 

 nearly stagnant, and the thickness at the lower end is relatively less 

 than that of a vigorous glacier. This is clearly not the case with the 

 glaciers of the first group; the ice is in motion, its slow movement 

 coming from slight slope and slight pressure; the debris is super- 

 glacial; the thickness at the lower end is considerable, and the front 



1 Except in form these glaciers might properly be classed with Piedmont glaciers, 

 which they strikingly resemble. See Russell, "Malaspina Glacier," Journal 0} 

 Geology, Vol. I. 



2 I. C. Russell, American Geologist, Vol. IX (1892), pp. 322-36. 



