ScHARFF — Origin of Irish Land and Freshtoater Fauna. 485 



west coast of Ireland was at a somewhat higher level than at present. 

 We should then have between the two countries a deep hollow, into 

 which rivers from both would pour their contents and form a large lake. 

 If the ancestors of the three species of Coregonus had lived in this 

 lake, it is quite conceivable that existence being rendered impossible 

 for freshwater fish after the breaking down of the southern land 

 barrier between Wales and Wicklow and the consequent encroachment 

 of the sea, they were driven to ascend the various rivers which flowed 

 into the newly-formed estuary. They eventually would have settled 

 down in some of the neighbouring lakes communicating with these 

 rivers. Two of the species, at any rate, are separated by such slight 

 differences in structure that a common origin at no very remote 

 period is easily recognizable. 



There are other forms of freshwater fish besides Coregonus, the 

 range of which in the British Islands can be easily explained by the 

 supposition of the Irish Sea having been the site of a former fresh- 

 water lake. I need only refer to the charrs — the peculiar species of 

 black trout — of which three closely- allied forms occur in Wales, Ire- 

 land, and the North of England. 



The results obtained from the inquiries instituted into the origin of 

 a portion of the Irish fauna are as follows : — Ireland was in later 

 tertiary times connected with Wales in the south and Scotland in the 

 north, whilst a freshwater lake occupied the present central area of 

 the Irish Sea. The southern connection broke down at the beginning 

 of the Pleistocene Period, the northern connection following soon after. 

 There is no evidence of any subsequent land connection between 

 Great Britain and Ireland. 



This report is necessarily a very short one, and is more in the 

 nature of a preliminary contribution. I propose shortly to lay before 

 the Academy a more detailed memoir on this subject, in which I hope 

 to give tables of the general range of the Irish mammals, reptiles, 

 amphibians, and fishes ; also maps illustrative of the geographical 

 changes which affected the British Islands. I hope also to submit 

 my views on the salient features of the physical geography of 

 Europe during recent geological times, based on the distribution of 

 animals. 



