9 26 Proceedings of the Royal Irish Academy. 



straits of the Atlantic, which form the entrances to Clew Bay. On the 

 north-east the nearest point to the island is the southern end of Achillbeg, 

 which lies about; three miles from Clare Island lighthouse, and the same 

 distance separates the Harboiir on the south-east corner of the island 

 from Eoonah Quay, near Louisburgh. Bocks projecting above the sea 

 in the channels to the north and south of the island show that the general 

 depth of the sea is not great, and suggest that at one time Clare Island was 

 either connected with the mainland or was only separated from it by narrow 

 straits joining in Clew Bay. This suggestion is strengthened by geological 

 evidence, 1 which goes to show that much of Clew Bay was once filled with 

 glacial drift after the disappearance of the main ice-sheet moving in a south- 

 westerly direction, while a subsequent local ice-sheet from the south passed 

 over the island from the Mweelrea group of mountains, the moraines of 

 which occupied the valleys of the rivers now running into the mouth of Clew 

 Bay in a north- westerly direction. There is good reason for supposing, there- 

 fore, that the last connexion between Clare Island and the mainland was on the 

 southern side, while the northern connexion was more or less interrupted by 

 the drainage system of the land lying to the north and east of Clew Bay. 



A comparison of the past and present forest flora of Achill Island and the 

 Curraun peninsula to the north, and the stretch of flat land between Louis- 

 burgh and the Mweelrea and Croaghpatrick mountains, and the character of 

 the soils in which this floi-a existed, renders it probable that the country to 

 the south of the island was more heavily timbered at an early period than 

 that on the Achill side. On the Louisburgh side, the soil is of a comparatively 

 fertile character,' and is highly cultivated. "While peat originally covered 

 the whole district in a general way, it owed its origin to the more or less 

 marshy character of the surface, which subsequent drainage was able to turn 

 into agricultural land, and on and under the peat Oak and Pine once 

 existed in large numbers, as is proved by the stumps now remaining. While 

 the whole area is wind-swept and bare at the present -time, it is evident that 

 the genei'al lie of the land, a considerable proportion of which slopes in an 

 easterly direction from the western coast-line, would, under existing climatic 

 conditions, allow trees of the same species to thrive at the present time if 

 planted in large masses. The existing tree-growth is chiefly confined to belts 

 and clumps round a few farm-houses, but at Old Head a considerable area of 

 native timber and plantation exists, and suggests that the present scarcity of 

 tree-growth on this side of Clew Bay is chiefly due to human interference, 

 and not to natural causes. On the sheltered side of Old Head, Oak, Ash, 

 Beech, Pine, Sycamor - e, etc., of normal dimensions are found, although rather 



1 Clare Island Survey, Part 7. 



