7 2 Proceedings of the Royal Irish A cadcnijj. 



island, rising to 729 feet above Ordnance datum. Both hills rise rapidly from 

 the general level of the ground, and are separated by a fairly wide hollow, 

 forming a gap that connects the comparatively low-lying northern and 

 southern areas. A steep scarp along the northern side of Knocknaveen 

 follows the course of a great zone of fracture which extends across the 

 island from north of the harbour to the western coast. 



The coast along the north and west is formed of precipitous rocky cliffs, 

 rising to considerable elevations. One of these, at Allahan, to the west of 

 Croaghmore, reaches the formidable height of 900 feet above the level of the 

 sea. The cliffs of the north-east coast, composed mainly of drift (see Plate I), 

 often attain a height of 60 or 70 feet: while those of the eastern and southern 

 coasts are comparatively low, rarely rising above the 50-foot contour - . 



The island is drained by several small streams. Two of these take their 

 rise in the watershed occupying the hollow between Croaghmore and Knock- 

 naveen ; one. the Doree Eiver, flows northward through Leearrow and 

 Maurn, and the other southwards through Strake. entering the sea near 

 Pitacurry. Another larger stream, the Owenmore, drains the south-eastern 

 slopes of Croaghmore into the sea at Ooghvunanal. The drainage of the 

 remainder of the island is effected by five or six streamlets descending from 

 Croaghmore and Knocknaveen, and two flowing through the townland of 

 Ballytoohy More. 



Three small lakes occupy the undulating ground to the north-west of 

 Knocknaveen, and another, Lough Avullin. is situated in the townlaud of 

 Maum, where the Pollabrandy streamlet joins the Maurn Eiver on its way to 

 the sea. 



A comparison of the geological structure of Clare Island, and of the wild 

 and nigged features of its scenery, with those of the neighbouring mainland, 

 shows clearly that the island once formed an integral part of the highlands 

 round Clew Bay. At what period of its history it first became isolated from 

 the mainland, it is impossible to say. It is probable, however, that in Lower 

 Carboniferous times it formed, if not an island, at least part of the shelving 

 shore-line of a western inlet of the sea that then extended over most of the 

 piesent Irish area. Confirmatory of this hypothesis, it will be seen, on 

 examination of a geological map of the Clew Bay district, that sandstones of 

 this date, typical shore deposits, occupy the north-east of Clare Island, and 

 fringe the Clew Bay basin on its landward side, except at its southern margin, 

 where the beds are partly cut out by a fault. These rocks must have been 

 laid down in close proximity to an old land-surface that partly enclosed the 

 Clew Bay inlet, and extended westwards over a considerable portion of the 

 present Atlantic area. 



