9 32 Proceedings of the Royal Irish Academy . 



regarded as bearing upon this point. Ash is probably the most common 

 indigenous tree in the Irish Mora at the present time, but does not appear to 

 exist on any of the western islands except where planted. Compared with 

 the Oak and Hazel, its facilities for dispersal by air and water are numerous, 

 while it thrives better in maritime districts than either, and the same 

 applies to the Wych Elm. Alder is almost as common as Ash on the main- 

 land, and both species are found at Old Head and Achill, probably native. 

 This species stands sea-wind better than any broad-leaved tree, and is now 

 being planted for shelter hedges on Clare Island with fair success. It also 

 distributes itself easily by wind, water, birds, etc., and, when once established, 

 is difficult to eradicate from damp ground. Amongst the numerous samples 

 of bog-timber collected by the writer on the island, no trace of Ash was 

 found, and it is reasonable to assume that this species never existed there. 

 It is highly probable, therefore, that the separation of Clare Island from the 

 mainland occurred during the movement of the present forest flora westward, 

 the earlier or more vigorous arrivals on the seaboard reaching the island, but 

 later comers being shut out by the sea-harrier subsequently formed. Several 

 of the Clare Island species, such as Holly, Mountain Ash, etc., may have 

 arrived at any time, as the distribution of these species by birds is constantly 

 going on ; but the presence of Oak and possibly Hazel on the one hand, and 

 the absence of Ash, Elm, &c, on the other, are inexplicable on any other 

 grounds than the above. 



The main conclusions which one arrives at from a careful survey of all 

 the facts regarding the past and present forest flora of Clare Island are : — 



1st. That the earliest tree-growth existed when Clare Island was con- 

 nected with the mainland, and that Pine and Birch were the 

 principal species. 



2nd. That the Oak and Hazel followed the Pine, and reached the island 

 before its connexion with the mainland was entirely broken oft'. 



3rd. That the Oak and Hazel gradually dominated the Pine, when the 

 former produced timber of medium size at an altitude of 400 feet 

 over present sea -level. 



4th. That the absence of Ash, Wych Elm, Alder, etc., from the whole of 

 the western islands suggests that these islands possess the oldest 

 representatives of the mainland forest flora only, and were separated 

 from the mainland at an early period. 



5th. That while the present stunted condition of tree-growth on the 

 island is partly due to human agency, there are good grounds for 

 supposing that the summers are cooler at the present time than 

 when the Oak occurred in comparatively large numbers, 



