9 30 



Proceedings of the Royal Irish Academy. 



attained its maximum encroachment on the land, as shown by the 25-foot 

 beach in the north-east of Ireland. Praeger 1 summarizes the climatic changes 

 corresponding to differences in the sea-level in this part of Ireland as 

 follows : — " The peat bed [containing a submerged forest of mixed Oak, Hazel, 

 Alder, Pine, &c], so far as we know its flora and fauna, points to a climate 

 not much differing from that which exists at present. A slight submergence 

 allowed the deposition of the lower estuarine clay, with its rather southern 

 fauna, and a further submergence was followed by the accumulation of 

 deposits of mud in the shape of the upper estuarine clay, of sand banks, such 

 as the Curran of Larue, and of shelly beach deposits, such as Portrush. At 

 this period the southern element of the fauna attained its maximum. Finally 

 came elevation of the land, and with the last change of level came the final 

 fluctuation in the character of the animal life — a distinct return towards 

 its former northern character, which has left the fauna as we now find it." 



Correlating the above changes in sea-level and marine fauna with the 

 growth of trees and peat on Clare Island, it is possible to imagine the 

 following succession : — 



Period. 



Sea-Level. 



Submerged or Peat 

 Forest Type. 



Peat Type. 



1 

 i 



•20 - 30 feet lower. Tine and Birch. 

 0-10 „ Mixed Oak and Pine. 



- 25 higher on ; Oak, Hazel, etc. 



north-east coast of 



Ireland. 

 Present level. Broad-leaved Scrub. 



Shallow Marsh Peat. 

 Deeper Marsh Peat. 

 Sphagnum Peat on Marsh bog. 



Mountain Peat in west of Ire- 

 land and at high elevations. 



While the above assumption regarding the succession of species appears 

 reasonable, it is evident that the general absence of the Oak at more than 

 ten feet below present high-water mark in Achill Sound does not explain its 

 introduction to Clare Island by a land-bridge towards the end of the rise in 

 sea-level. There is, however, proof of the existence of the Oak in the southern 

 parts of Ireland when the sea failed to reach the present low-water mark. At 

 Arclmore, County Waterford, no trace of Pine can be seen, while Oak, 

 Birch, &c, extend under the present sea-level, and at Bray and several other 

 places Oak, &c, appear to go much lower than the ten feet assumed above. 

 But a possible explanation of the late introduction of Oak into the island by 

 land is the strong probability of any land-bridge having partially survived the 

 rise of the sea for a long period, owing to the time required to completely eat 

 away eight to ten miles of Boulder-clay. There is every probability, again, 

 that the bed of the channel between Clare Island and the mainland has been 

 1 Proc. P. I. A., Scries iii, vol. iv. 



