94 A SUMMER IN GREENLAND 
of a lost vegetation contained in the sandstones and 
associated shales suggest a scene very different 
from the present—a time when the rocks of the 
valley were slowly accumulating, as gravel, sand, 
and mud, in the delta of a river flowing between 
banks clothed with a rich and varied vegetation. In 
Greenland to-day the vegetation lives precariously 
on the rocks which were uplifted from the water 
some millions of years ago. Higher up the ravine 
lavas and beds of ash spread in a succession of 
layers over the sedimentary rocks recall a period 
of intense volcanic activity and, most eloquent of 
all, the towering weather-beaten walls of basaltic 
dykes compel the mind ofan observer, familiar with 
ordinary geological evidence, to picture fissures 
riven in the strained sandstone filled with molten 
basalt welling up from a subterranean reservoir. 
These glimpses of the past and their disharmony 
with the present impart to the reality of geological 
history a sense of unreality, an impression that 
may best be expressed by one of the conceptions 
of Milton: 
Thither, by harpy-footed Furies haled, 
At certain revolutions all the damn’d 
Are brought; and feel by turns the bitter change 
Of fierce extremes, extremes by change more fierce, 
From beds of raging fire to starve in ice 
Their soft ethereal warmth, and there to pine 
Immovable, infix’d, and frozen round, 
Periods of time; thence hurried back to fire. 
On the left-hand side of the cliff rising from the 
beach (Fig. 45) a dyke cuts obliquely across the 
almost horizontal Cretaceous sediments, while other 
