438 Proceedings of the Royal Irish Academy. 



But when we come to the less coiispicuoiis Invertehrates, we are 

 confronted with cases which give us even less chance of escaping 

 from the inevitable assumption of a land-connexion with the Continent. 

 How are we, for instance, to suppose that earth-worms reached 

 Ireland, or Testacella, a slug-like mollusc, which spends its entire 

 existence under ground, or Platyarthrus Hoffmansegyii, a blind wood- 

 louse, which also lives below the surface of the soil, in the nests of 

 ants, unless by slow migration on land ? Having decided then that 

 the bulk of the Irish fauna migrated to Ireland on land, we have 

 next to consider what was the nature of that land-connexion before 

 we proceed to discuss the views as to the time when the migration 

 took place. 



On the Nature of the Lani- connexion. 



Prof. J. Geikie refers to the now submerged land between Great 

 Britain and Ireland in the following terms (35«, p. 248): "If the 

 whole area of the British Islands were elevated so as to convert the 

 adjoining seas into dry land, we should find an elongated lake extend- 

 ing from the Scottish Highlands southwards to the regions between 

 "Wales and AVicklow county in Ireland, a length of not less than 

 240 miles, with a maximum depth of 594 feet." In a beautiful map, 

 reduced from the Admiralty charts, Prof. Geikie gives still more 

 details, Tlie soutlicru shore of the lake was in the latitude of 

 Wicklow. It then stretched almost due north, sending off an arm 

 towards the Firth of Clyde, and another to the Sound of Jura. 

 The extreme north-west shore was situated between the Co. London- 

 derry in Ireland and Argyl(;shire in Scotland. A little further to the 

 west lay the watershed which divided the rivers draining into the 

 lake to the east from those flowing directly west towards the Atlantic. 



Such an elevation of land, as that described, is supposed by 

 Prof. Geikie to have taken place after the Glacial Period, and Mr. 

 Kinahau's views agree with this in the main points (51 V). Prof. 

 E. Forbes believed that some of the Irish plants at present confined 

 to the west coast arrived long before the rest of the fauna and flora. 

 (33 rt, p. 14). According to his theory there was, at an ancient p re- 

 Glacial Period, a geological union or close approximation of the west 

 of Ireland with the north of Spain. The flora of the intermediate 

 land was a continuation of the flora of the peninsula. The destruc- 

 tion of this land had taken place before the Glacial Period, but a 

 number of the southern species had meanwhile reached Ireland. 

 Only the relics, he thought, of this most ancient of our island floras 



