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Ayyendices to Twenty-first Annual Report 



till a summer flood permits ; but arguing from analogy I am inclined to 

 believe that even if the fall was rendered much less serious, the fish 

 would not ascend till the wintry thermal conditions had entirely left the 

 water. The river Brora is an example of another spring river where a 

 comparatively insignificant fall is sufficient to check all fish till May. In 

 reverting now to the case of Loch Tay and the Dochart we find that 

 similar conditions are found there also. There is a fall at, or just above, 

 Killin. In all these cases it seems to me we have fish ascending till they 

 are checked by colder water and an obstruction. In no case is an attempt 

 made to ascend till either a rise of water-level occurs simultaneously with 

 a rise of temperature, or till the river water has lost its wintry character. 

 Andjustasa flooded condition in a comparatively small river has its 

 influence upon the ascent, so it appears that in rivers of large volume, 

 such as the Tay, obstacles such as the Linn of Campsie or the rocks at 

 Grandtully are more readily surmounted than would be the case in 

 smaller waters. 



