502 Proceedings of the Royal Irhh Academy. 



forms were probably to a great extent exterminated, but, as soon as the 

 eastern current diminished in strength, the southern species -^oiild 

 seek to return to their old quarters. Finally, when the old land- 

 connexion between Scotland and Scandinavia broke down, the waters 

 of the !N"orth-European Sea found an outlet in that direction, and 

 brought Arctic species directly into the iN'orth Atlantic. "WTien at last 

 Scotland and Ireland became separated, a northern fauna would once 

 more supplant the southern one in the Irish Sea. Thus, I think, ITr. 

 Praeger's conclusions as to the changes in the marine fauna of the 

 north-east of Ireland agree in the main points with those which I 

 arrived at from an independent inquiry into the origin of the terres- 

 trial faxma of that island. 



From the careful study of terrestrial faunas, indeed, has been 

 gained not only the knowledge of the changes of climate which have 

 passed over the world, but, in the main those geographical revolutions 

 which have been produced in^NTorth Europe in recent geological times. 

 To put our knowledge of the origin of the European fauna on a firmer 

 basis has been my object in this memoir, and, although much work 

 still remains to be done in clearing up obscure points in its history, I 

 hope that I have clearly indicated the manner in which future research 

 should be conducted. 



I trust also that I have succeeded in strengthening the old Lyellian 

 theory on the origin of the Glacial Period which has received such 

 strong support from no less an authority than Lord Kelvin (87). 



Summary. 



p. 427 In this paper I have endeavoured to show how the present fauna 

 of Europe originated. For that purpose it was found advisable to 

 commence the inquiry by the study of the past and present fauna of 

 an island. The British Islands, and in particular Ireland, seemed to 

 me most suitable for that object. 



p. 432 The fauna of Ireland as well as the flora is found to consist mainly 

 *? of two elements, one of which camefi'om the north and the other from, 

 the south. In the fauna of Great Britain the same two elements, 

 occur, but there is, ia addition, athird — an eastern one — chiefly confined 

 to the eastern counties. The southern element contains aninialswhicli 

 came originally from South-western, and others which migrated to the 

 British Lshinds from the South and Central Europe. The former are 

 confined to the south-western counties of England and Ireland, whilst 

 the latter are chiefly found in the south-west of England, "Wales^ 



