60 ON THE PARALLEL ROADS 



original lake was nearly so profound in that quarter. The 

 sudden burst of the water must have done much to scoop it 

 out almost instantaneously, and the river itself would continue 

 active in reducing it, in a proportion exactly equal to the 

 quantum of its deviation from a regular declivity, counterba- 

 lanced as it might be, by the various degrees of hardness of 

 the materials through which it had to work. These last ob- 

 servations apply equally to the effects which must have been 

 produced by the rivers of all the glens, after the evacuation of 

 their lakes. We see how the rocks have been cut in the de- 

 scent of the stream from the High Glen, which must have 

 been done in the same manner I have just described, after 

 the water escaped from the Bay of Turret. So, after the 

 subsidence of Loch Roy, which laid dry all Upper Glen 

 Roy, the stream would, in the same way, begin to cut the 

 ravine, to the south of the rock, dividing Upper and Un- 

 der Glen Roy ; and the operations there, would be increa- 

 sed by the farther reduction of Loch Roy, to the level of Loch 

 Spean. The inclined shelves opposite to the mouth of Glen 

 Turret (See the diagram, Plate VII. fig. 6.) are evidently 

 the effect of the water of Loch Roy, rushing off at successive 

 elevations, during its final evacuation ; or perhaps, indeed, 

 some of the lower ones may have been owing entirely to the 

 after operations of the river. Generally towards the mouth of 

 Glen Roy, and particularly to the eastward of the Hill of Bo- 

 huntine, the valley has been much deepened by the river, and 

 the rocks are more and more cut, as it proceeds in its progress 

 down the glen ; we are not, therefore, to decide upon the 

 depth of the ancient lake at this point, by what we now see. 

 The same deepening of the channel of the river takes place in 

 the common valley of the united Roy and Spean, as is exem- 

 plified in the wild scenery at Highbridge, to which direction 

 the river Pattaig was turned, and whither the whole water of 



these 



