GEOLOGICAL EFFECTS 187 



should be selected which will most readily and natur- 

 ally attract the attention and excite this destructive 

 impulse of the salmon. 



It is recognized that certain peculiarities of colour 

 are more favoured by the attention of the salmon in 

 some than in other rivers, although the natural life 

 existing in the different waters is identically the 

 same. 



It has occurred to me that this partiality by the 

 salmon for certain colours in certain streams may be 

 due to the different effects produced on the subaqueous 

 appearance of water life by the geological strata of the 

 country affecting the bed and the banks of the river, 

 the natural differences of the foliage and the vegeta- 

 tion through which it passes, and its altitude above 

 the sea. 



Cloud and sunshine, clear or thick water, sunlight or 

 shade, reflection or shadow, depths or shallows, forest 

 or open country, rapid or slow current, will all be 

 varied by the above factors, and natural phenomena 

 will, therefore, tend to alter at least the appearance, if 

 not the colour, of the subaqueous life in different 

 waters. Whatever purpose the salmon has in his pur- 

 suit of a moving object, it is certain that unless scared 

 by former experience, he will most readily attack the 

 object which has the most natural appearance and 

 movement. 



As the ever- varying influences of natural and 

 meteorological phenomena will affect the colour of 

 moving objects, as hunger may not be the reason of 



