Rcvpiditii of Weafften'iiy in Arctic Lat if rides. — Tarr. 183 
during the winter the minerals must become brittle, and this 
result may also aid in the breaking up of the rocks; for when 
a rock is extremely brittle the strains caused by contraction, 
resulting from continued cold, will then be much better able 
to break off fragments than at other times. Whatever the 
exact cause, flakes, bits and even blocks of large size are riven 
from the ledges and cliffs. Even on horizontal surfaces one 
often sees remarkable instances of the spreading of rocks, 
evidently as the result of frost action, on the joint and bed- 
ding planes. Great blocks have moved horizontally for dis- 
tances of several inches, or even in some cases a foot or two; 
and upon gentle inclines the down hill sliding of disturbed 
blocks is evidently rapidly in progress. 
Upon steeper slopes the blocks fall as soon as they are 
loosened from their beds. In both Greenland and Baffin land, 
although I'ecently ice covered, and certainly scoured sufficiently 
to remove the loose materials, the most characteristic surface 
feature, besides that of the bare rock ledges, is the talus ac- 
cumulation at the base of the cliffs and on the sides of hills. 
One can rarely travel in ^,ny direction without very soon hav- 
ing his path leading him over a talus of frost-riven boulders: 
and so rugged is the surface as a result of this that the aver- 
age rate of travel over the land in the part of Greenland 
where our party worked was not over one or one and a half 
miles an hour. In these talus deposits the surface of the 
blocks is usually rusted by iron salts derived from the chemi- 
cal changes which are in progress, and they are generalh^ 
covered with lichens; but every now and then single blocks, 
or areas of blocks, of fresh gneiss mark the recent falls from 
the cliffs above. Upon gentle slopes talus blocks are present 
and evidently moving down hill. Everywhere frost and cold 
are at work on a grand scale. 
The talus slopes are often combined with a ruggedness of 
topography quite out of harmony with the outline of a glacia- 
ted country, as we commonly understand it. Some of this rug- 
gedness is an inheritance from pre-glacial times. In fact the 
great cliffs, hill slopes and valleys, and even many of the 
moderate features, are thus inherited. In many places the ice 
action has not been sufficient to greatly smooth the surface. 
However, much of the irregularit}' is distinctly of post-glacial 
origin. 
