274 BRITISH FRESHWATER FISHES 



culminating in the union of our islands with each 

 other and with the Continent, and then a subsidence 

 followed which gave to our islands approximately 

 their present outline. 



Speculations as to the exact time occupied by 

 these changes are futile, but it is probable that the 

 whole duration of the Tertiary Period should be 

 expressed in tens of millions of years and that of 

 the Glacial Epoch in tens, or at most hundreds, of 

 thousands. Possibly about 100,000 years may have 

 elapsed since the end of the Glacial Epoch, and our 

 final separation from the Continent was of still more 

 recent date. 



As soon as the ice-sheet had begun to disappear 

 Char must have commenced running up into the 

 lakes which were formed, and as the elevation of 

 the land proceeded new lakes appeared and in turn 

 became inhabited by Char. All this time the climate 

 was gradually getting warmer, and the southern limit 

 of anadromous Char was receding northward ; then 

 the Sea-trout reached our islands, and these in turn 

 began to form fluviatile colonies in our lakes and 

 rivers. 



At the present day the southern limit of anadromous 

 Char, namely, Iceland and the northern coasts of 

 Europe, nearly coincides with the northern limit of 

 anadromous Trout. Thus we can understand why 

 some of our lakes contain Char, but no Trout. 

 Troutless lakes are fairly plentiful in the Highlands of 

 Scotland, although their number has greatly decreased . 

 in recent years through stocking with Trout. In 

 Ireland, Lough Gortyglass in Clare is an example of a 

 lake which contains Char, but had no Trout until they 

 were introduced about thirty years ago by Messrs. W. 



