GEOGRAPHICAL DISTRIBUTION 275 



and F. B. Henn. The latter gentleman tells me that 

 there is a fall almost immediately below the lake in 

 the stream which flows out of it and enters the estuary 

 of the Shannon, and that this fall is too steep for 

 Trout to ascend, although they are plentiful enough 

 below it. It seems probable that Char entered Lough 

 Gortyglass at a time when arctic conditions were 

 prevalent and the lake was almost on the sea-level ; 

 the subsequent elevation which brought lakes such 

 as Corrib and Currane into existence may have 

 formed the falls which barred the entrance of Trout 

 to Lough Gortyglass when the commencement of the 

 amelioration of the arctic climate brought Sea-trout 

 to the shores of Clare. The lake is now situated at 

 an altitude of from 200 to 250 feet above the level of 

 the sea, a less elevation than one would anticipate for 

 a troutless lake so far south, if movements of elevation 

 and subsidence had been nearly uniform over the 

 British Isles since the Glacial Epoch began to pass 

 away. Indeed, the absence of Trout from Gortyglass, 

 as well as the presence of Char in lakes scarcely 

 above the sea-level in Galway and Kerry, leads me 

 to believe that the subsidence that succeeded the 

 elevation that joined Britain to Ireland and to the 

 Continent has been greater in the south and west of 

 Ireland than in any other part of the British Isles. 

 The Whitefish probably established themselves at 

 about the same time as the Char, before the arctic 

 conditions had passed away. 



When the elevation had reached its maximum and 

 our islands once more formed part of the Continent, 

 the coast-line may have approximated to the 100 

 fathom contour. Our eastern rivers were tributaries 

 of the Rhine, which flowed northward along what is 



