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 of an 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 



