72 THE SALMON RIVERS OF SCOTLAND 



of the Tay at Meikleour, however, one realises that, even with a 

 greatly improved mouth, the Isla must always take a very subordi- 

 nate place. At present the Isla is so uniform and canal-like in 

 character that the creation of a more attractive mouth is a 

 matter of some difficulty. If a contraction of the mouth were 

 resorted to in order to concentrate the current, some precaution 

 would also have to be taken to prevent this simply resulting in a 

 further deepening of the river and an ultimate return to the present 

 sluggish character. 



EIVER TUMMEL. 



If a glance be taken at the catchment basin of the Tay, and the 

 disposition of the chief lines of water-flow noted, the central line 

 will be seen to be that of Glen Garry and the lower Tummel to the 

 Tay at Ballinluig the line traversed by the Highland Eailway. 

 The direction of this central line is rather singular, being south-east, 

 for the main axis of the mountains are at right angles to it. The 

 composition of the hills plus the glacial erosion are no doubt respon- 

 sible for the existing conditions, the rocks of the region being of 

 very different consistency and capable of resisting the action of ice 

 or of water to very different extents. The erosion of the Loch Tay 

 and Glen Dochart area is more advanced, however, than that of the 

 Tummel or Garry, and the main line of the Grampians cuts off 

 Loch Ericht from the source of the Garry, and still forms a high 

 and hard ridge. The Tummel, and to a greater extent the Dochart 

 and Loch Tay, secure much greater length by having been forced, 

 as it were, to flow to the central line from a west and south-west 

 direction. 



The direction of the Tummel is to the east throughout almost its 

 whole course. It rises from a number of small lochs lying in glacial 

 moraines in the Black Mount, south-west of the Moor of Eannoch, 

 and not far from the head waters of the Orchy. The furthest back 

 source is the stream called the Ba, which rises about three miles 

 west of the road from Loch Tulla to Kingshouse at the head of 

 Glen Coe, and flows into Loch Ba, thence into Loch Laidon, and so 

 on to Loch Eannoch. This region, at the glacial period, seems to 

 have been a sort of cap or ice-shed from which the ice moved in 

 various directions. Geological maps indicating glacial drift show 

 that ice moved, in the time of confluent glaciers, after the climax 

 of the Ice Age, down the line of the Tummel, down the Lyon, into 

 the Loch Tay region, and also down upon Loch Tulla and Glen 



