BIOLOGICAL VALUE OF TIIK WAUFAKK 249 



by natural agency, let me describe a change 

 which has taken place in a comer of Co. Donegal. 

 The promontory of Horn Head is bounded on 

 the west by < \ tensive sand-hills, 100 ft. or more 

 in height. On the southern side it is divided 

 from the mainland by a channel, which narrows 

 down to 100 yards or so in width where it 

 fringes the sand-hills, and then widens out again, 

 covering an area of approximately 270 acres. 

 As far as is known in the memory of man, this 

 area has always been tidal. But in recent years 

 a change has taken place, and the blown sand 

 has silted up the channel, with the result that 

 this tidal area has been transformed into a 

 brackish lake. What has brought about the 

 change is not easy to determine. There is 

 evidence, however, of a slow alteration of the 

 level of the shore-line ; for in the midst of the 

 sand-hills, situated 150 yards or so from the 

 present sea-margin, and running parallel with it, 

 there is an accumulation of pebbles some 3 feet 

 high by 4 feet deep. This raised beach is now 

 separated from the Atlantic by sand- drifts of 

 considerable height, and consequently there are 

 some grounds for believing that secular elevation 

 is taking place, which, if it be the case, will 

 account for the change in progress. Now the 

 effect on the bird population can be seen even 

 now, and will doubtless become more apparent 

 as the years pass by. Sand-Martins used to find 

 plenty of places to breed amongst the sand- 

 drifts, and moreover do so still. But their 

 nesting sites are constantly changing and dis- 



