Clare Island Survey — Tree-Growth. 9 31 



deepened by tidal scour during the last two or three thousand years, so that 

 the fall in sea-level necessary to lay dry the present channel has only partly 

 to do with the problem. Another point necessary to bear in mind is the fact 

 that the submerged forest and peat layers in Blacksod Bay and adjoining areas 

 were formed at a time when higher ground, in the shape of sand, gravel, or 

 clay ridges, must have existed in a seaward direction, otherwise the formation 

 of marsh and peat could not have occurred. Many of the trees and the 

 overlying or surrounding peat may thus have grown on a surface actually 

 below high-water mark, and not been submerged until the barriers on the 

 sea side had been broken through by erosion. The appearance of having 

 grown on a surface sloping gradually down to and under the sea, which 

 these submerged forests now present to the eye, may lead to quite 

 erroneous ideas being formed of the rate at which the sea advanced, and 

 it is highly probable that this occurred in the form of a series 

 of jerks instead of as a gradual and steady advance. Land may 

 thus have existed several miles to seaward until quite recent times, 

 and afforded a foothold for Oaks on islands and peninsulas no longer 

 in existence. A familiar example of the above condition of things may be 

 seen between Greystones and Wicklow, where the sea has encroached nearly 

 a mile within the memory of those now living, and where the ridge on which 

 the railway runs is the only barrier against further encroachment. 



The possibility of the introduction of the forest flora by wind, water, or 

 animals has been fully discussed by Praeger, 1 and, so far as many species are 

 concerned, presents little difficulty. But Oak and Hazel, the two most 

 significant components of the present forest flora, cannot be distributed by 

 wind, while ripe acorns and nuts sink rapidly after immersion in water, and 

 it is unlikely that they would, in the event of their floating, get beyond the 

 high-water mark of any shore-line on which they were cast up unaided. No 

 bird exists which would be likely to carry nuts, and although acorns are 

 frequently carried by Books two or three hundred yards for more convenient 

 consumption, the chances of their carrying them over two or three miles of 

 sea are very remote. Acorns may be carried in an undigested state in the 

 crops of Pigeons, but the death of the birds shortly after a meal would be 

 necessary to enable them to germinate. The chances of the introduction of 

 these species by any other than overland routes are, therefore, too remote to 

 be accepted as foregone conclusions, more especially as Clare Island appears 

 to be the only island on the western seaboard which contains Oak, although 

 Hazel has been recorded also from Inishturk by Praeger. 2 



The absence of several mainland species from Clare Island may be 



1 Clare Islam! Survey, Part 10. - Irish Naturalist, vol. xvi. 



