OF GREAT BRITAIN. 9 



is often the case in rivers issuing from large lakes, 

 in which the water has previously undergone a sort 

 of filtering process and has become warmer, owing 

 to the greater mass and higher temperature of its 

 source ; whilst, on the other hand, streams which 

 are liable to be swollen by the melting of snows, 

 or cold rains, or which are otherwise bleak and ex- 

 posed, are later in season, and yield their principal 

 supply when the great lake rivers are beginning to 

 fail. 



The order in which fish ascend rivers is allow- 

 ing for the variations already pointed out gene- 

 rally somewhat as follows : 



First come the strong, early runners. These are 

 succeeded by the Grilse, and by the small " Spring 

 Salmon " which have probably never ascended at 

 all as Grilse, but have remained in the sea since 

 the Smolt state a period of from eight to ten 

 months, as noticed in " Proved Facts," No. 10. 

 The scales of these spring Salmon are not easily 

 rubbed off like those of the Grilse, and their tails 

 are not so forked. A few of them generally appear 

 with the early-running fish. As the season ad- 

 vances, the larger fish and those heavy with spawn 

 begin to work their way upwards from the mouths 

 of the rivers and estuaries towards the higher 

 reaches ; and such fish continue ascending from the 

 sea until the close of the autumn, or, if the river be 

 an early one, of the summer. 



Even as late as November and December, and 



