A MOUNTAIN TARN, 171 



veloped since that time. Indeed, even if 

 the lake had been here before the glacial 

 epoch, the ancestors of these trout could not 

 have dwelt in it ; for we know that every 

 species of animal now living in Britain must 

 necessarily have entered the island since the 

 ice-sheet cleared away. 



How did the trout first get into the tarn } 

 That seems at first sight a difficult question, 

 for the only stream that communicates with 

 it is the little torrent, broken by a hundred 

 small cascades, which drains its waters into 

 the river below. No fish could now possibly 

 leap up these continuous waterfalls from 

 ledge to ledge, some of them as much as 

 twenty or thirty feet high. Hence local 

 naturalists have speculated not a little on the 

 origin of the trout, one theorist suggesting 

 that they were carried hither by a water- 

 spout, another that the eggs were brought 

 into the pool clinging to the feet of a water- 

 fowl, a thira that the ancestral fish were 

 placed in siltc by the finger of the Almighty 



