Clare Island Surrey — Geology. 7 9 



The splendid work of the Belfast Naturalists' Field Club in investigating 

 the distribution of the " erratics " in the drifts of the north of Ireland 

 enables us to trace the Scottish glacier approximately to its western limits. 

 Fragments of the unique riebeckite-eurite of Ailsa Craig, which have been 

 found so persistently in the drifts of the north-east of Ireland, do not appear 

 to have been carried very far westward into the country. " In spite of care- 

 ful search, Mr. Eobeit Bell never found any west of the Bann until this year 

 (1906), when he picked up a solitary piece on the shore of Lough Neaghnear 

 Moyola River." 1 Since then, however, Ailsa Craig " erratics " have been 

 recorded from Limavady and Kilrea, and, quite recently, the known area of 

 their distribution has been extended westwards to Moys, about three miles 

 S.S.W. of Limavady, where a specimen of the rock was found by Madame 

 Christen, of the Belfast Naturalists' Field Club, at an elevation of over 400 

 feet. Judging from the distribution of these foreign boulders, it seems 

 likely that a line running south-east from the mouth of the river Foyle 

 marks approximately the limit to which the Scottish glacier penetrated into 

 the country. 



The great central Irish snow-shed occupied comparatively low ground 

 south of the Ox Mountain range, and extended along an axis running north- 

 east and south-west from Lough Neagh to Lough Corrib. From this axis 

 the ice moved towards the sea in all directions, swamping the whole of the 

 present Irish area, and passing at its north-eastern and eastern margins into 

 the Scottish glacier. Westwards it overspread the highlands of Connaught 

 and extended far into the sea along the present submarine plateau, probably 

 reaching the 200-fatliom line at the edge of the Atlantic abyss. 



This description represents briefly the condition of north-western Europe 

 during the period of maximum glaciation. From whatever cause, the ice, as 

 has been seen, developed in a south-westerly direction from its Scandinavian 

 focus, fresh centres of distribution arising as it proceeded along its course ; 

 but the ice from all sources united to form one general ice-cap which com- 

 pletely buried both sea and land north of a line running east and west along 

 the valley of the Thames. 



During the period of maximum ice-development, Clare Island and the 

 Clew Bay area were overwhelmed by the Central Irish Glacier which invaded 

 the district in a direction a Little south of west. Confirmatory of this 

 hypothesis, it may be mentioned that the principal glacial phenomena of the 

 island indicate a great ice-movement seawards in this direction. Thus the 

 rocks of the low platform along its southern shore are deeply furrowed and 

 polished by ice that moved out to sea in a direction bearing 10° to 15° south 



1 Proceedings of Belfast Naturalists' Field Club (1906), vol. ii, p. 324. 

 R.I. A. PnOC, VOL. XXXI. B 



