I9I0.] INLAND-ICE OF THE ARCTIC REGIONS. 109 



out by a number of observations. Newly fallen snow in Canada 

 has a density of about o.i. Over the level surface about Winnipeg 

 in the month of January and at a temperature of io° F., the snow 

 was found to have a density within the upper two feet of 0.38; 

 while in the woods at the same time and at the same depth, here 

 without a crust, its density was 0.19. Thus it is seen that the snow- 

 in the woods is about twice as heavy as newly fallen snow, but only 

 about half as heavy as that which has been chased about by the wind. 

 At Glacier House in the Selkirks, where the snow is shielded from 

 the wind within a narrow valley, experiments showed a density of 

 0.106 at the surface, whereas at a depth of one foot below the sur- 

 face the density was 0.195, ^"d at a depth of four feet, 0.354. 

 The middle value being that of the snow in the woods at Winnipeg, 

 it is seen that the weight of an additional three feet of snow is 

 necessary in order to pack snow as tightly as is done by the wind 

 blowing over the prairie. After a time, as a result of this treatment 

 by the wind, an eight-inch snowfall dwindles by packing in the 

 woods to four inches, and over the open plain to a two-inch layer. 



In eroding a drift, the wind first attacks the softer surface layer. 

 This removed, the snow of the blast adheres less to the surface of 

 the drift, and in consequence abrades it more vigorously. Thus, 

 notches in the ridges, instead of being mended by the detritus, are 

 increased by it, and transverse ridges are presently cut through, and 

 we pass by stages from an arrangement of ridges transverse to the 

 wind to that of longitudinal structures having the greatest exten- 

 sion parallel to the wind.^^ These longitudinal sastrugi appear to 

 be the dominant ones, and from them the direction of prevailing 

 winds may be determined as has been already proven in the Antarc- 

 tic. On the Siberian tundras the sastrugi are often the only guides 

 of direction which the natives have.^^ 



Source of the Snoiv in Cirrus Clouds. — What has been learned 

 of the circulation of air above the continental ice of Greenland 

 makes it extremely unlikely that any such excessive alimentation 

 upon the eastern margin through ordinary snow fall, as has been 



" Cornish, /. c, pp. 159-160. 

 " Tschirwinsky, /. c, p. 107. 



