2/6 BRITISH FRESHWATER FISHES 



now the bed of the North Sea ; we may suppose that 

 they received from the Rhine all the fishes which then 

 inhabited it and which were able to ascend them ; 

 but that the rivers of Eastern England should have 

 received so many fishes and those of Scotland so few 

 is not a little curious. Of course, in those days the 

 rivers of Scotland had not cut their way down to their 

 present level and were more rapid, but this must also 

 have applied more or less to those of Yorkshire, and 

 one cannot help feeling that if sluggish fish like Bream 

 and Rudd were able to establish themselves in the 

 latter, the lively and active Dace ought to have got 

 into the former. I rather incline to the theory that for 

 this last brief union with the Continent the 4<>fathom 

 rather than the loo-fathom line may represent the 

 coast in the North Sea area, and this seems to me in 

 harmony with the geological evidence that elevation 

 and gain of land has proceeded in the north of Britain 

 since it became an island. 



In the south-west the loo-fathom line may well 

 represent the former coast-line, and there can be little 

 doubt that our southern rivers received fishes from 

 the northern rivers of France via the " English 

 Channel River." This fish-fauna was evidently a 

 poorer one than that of the Rhine, but probably 

 most of the true freshwater fishes of the Stour 

 and Avon came to them from this source, and the 

 comparative poverty of the fish-fauna of Devon 

 and Cornwall is due to the unsuitability of their 

 small and rapid streams for most of the species, 

 although here, in contrast to Scotland, the Dace is 

 indigenous. 



A glance at the map will show that Ireland 

 probably got its fishes via the Irish Channel River 



