92 A SUMMER IN GREENLAND 
The main ravine at Atanikerdluk (Fig. 45) is 
not only of special interest geologically; it also 
affords a most remarkable display of dykes and 
illustrates on a grand scale the relation between 
scenery and rock structure. A stream flows among 
jumbled heaps of boulders at the bottom of a 
steeply inclined valley; the valley slopes consist of 
natural embankments of loose, light yellow sand 
mixed with milk-white rounded pebbles of quartz 
—detritus formed by the erosion of the sandstones 
which are here the dominant rocks—and in places 
the talus slopes are replaced by exposures of the 
rocks themselves, thick beds of sandstone with no 
division into layers, thinner, well-stratified beds, 
bands of shale, and an occasional seam of coal. 
These sedimentary strata, having a total thickness 
of many hundred feet, exhibit here and there on 
an exposed plane of bedding a series of ripple- 
marks, and afford other evidence of their origin 
as sheets of sand and mud in shallow water and 
among drifting currents. Many of the sandstones 
are made up of thin layers, often rendered more 
conspicuous by the presence of iron-stained bands, 
which exhibit the well-known arrangement spoken 
of as current-bedding: a series of layers sloping at 
a certain angle is cut off by another set sloping in 
a different direction. This frequent variation in 
the lie of the thin beds is evidence of the deposition 
of the sandy sediment in water with eddying and 
shifting currents. Dark brown dykes cut across 
the sands and sometimes intersecting dykes pro- 
ject like part of a huge network; but the most im- 
