Denudation at Cultra^ Co. Down. 17 



the solid rocks, and the transportation of their material, he 

 also saw the source of our beautiful systems of mountains 

 and valleys, of hills and fertile plains. He thus opened up 

 the border land between geology and i)hysical geography, 

 and gave an impetus to the fascinating study of those epigene 

 or surface agents, which in the present, as in the past, arc 

 altering and moulding the scenery of our globe. Their work 

 is constant; denudation and erosion are always in progress. 

 Each mountain rill, each wave that beats against our coast, 

 each shower of rain, leaves a mark upon the surface of the earth. 



The effects may be too faint for our obser\'ation, or for the 

 observation of generations, but the geologist sees the accumu- 

 lated results in the deep fissures of the mountain, in the indented 

 shore with sea- worn cave and isolated stack, in the pinnacles 

 and hillocks that lend such varied form and beauty to the 

 undercliff. And further still, along great lines of coast, far 

 above the highest tide-level, caves, escarpments, and suc- 

 cessive gravel-capped terraces bear testimon}- not only to the 

 erosion of former periods, but also to vast movements of eleva- 

 tion, interrupted by long periods of rest, probably also by 

 periods of temporary subsidence. 



From the raised beaches of our own coasts to the great 

 terraces of Patagonia, rising like mighty steps one behind the 

 other, we see the effects of the same co-operating actions — 

 erosion, deposition and upheaval. So also in the present, we 

 know that some regions of the earth are relatively rising, others 

 are gradually sinking; the sea is making encroachments on 

 certain coasts, it is receding on others. As a general rule, 

 where the rocks are hard, erosion is slow, where they are soft 

 and more easily disintegrated, it is rapid. 



Striking illustrations of marine erosion might be drawn from 

 the tunnelled caves and imposing sea-stacks of our Irish coast, 

 but the encroachment of the sea at Cultra Bay, on the southern 

 side of Belfast lyough, to which I wish to draw attention in the 

 present paper, has left no such impressive features. 



Much land has been washed away, of which no trace would 

 have remained, had it not been for one insignificant land-mark, 

 and before it too disappears, I have made a few notes of the 

 encroachment of the sea to which it testifies, which I hope 

 may not be devoid of interest. 



The landmark to which I refer is a shaft of crown Memel pine. 



