78 A SUMMER IN GREENLAND 
often basalt, that has been formed by the slow 
cooling and crystallisation of molten material 
forced from below through cracks and fissures in 
the overlying strata. The softer rocks fall an easier 
prey to the action of the weather than the harder 
and more compact dykes which are left as great 
ribs or dark brown buttresses projecting on a light 
yellow background of less resistent material. 
The photograph reproduced in Fig. 35, taken 
near Skansen, a small Settlement on the south-east 
coast of Disko Island, shows in the distance the 
basaltic plateau with an occasional glacier descend- 
ing from the inland ice; in the foreground the 
sloping sides of the valley are formed of light 
yellow sandstones and beds of dark shale which at 
a higher level are covered and protected by vol- 
canic rocks that were formerly continuous with the 
rest of the plateau. A cap of dark brown rock, 
part of a basaltic dyke, has saved the small hill of 
sandstone in the middle of the valley from the 
destructive action of weathering agents. Fig. 36 
shows a much narrower zigzag valley eroded by 
ice streams through the sandy sediments; the cliffs 
in the foreground have been weathered into 
slender pinnacles and intersecting ridges; a little 
lower down the ravine a brown jagged dyke of 
basalt casts its shadow on the sloping surface of a 
smooth embankment of light yellow sand, and the 
sides of the farther hill are scarred with a succession 
of small gulleys. Beyond the lower heath-covered 
ground lies Disko Bay with scattered icebergs, 
and on the opposite shore, too far away to be seen 
