OF THE EARN AND TEITH. 



163 



mark, this is shown. The highest bank c is only twenty -four feet above the river, 

 while the lowest a is six ; but the opposite side shows an intermediate level b 

 of some twelve or fourteen feet. The whole are thus on a very inferior scale. 

 Perhaps it may be thought that this diminution is due to the greater width of the 

 valley. But a still stronger reason, I believe, is the comparative weakness of 

 the current arising from the lower gradient of the incline along these portions 

 of the river course. To this I shall again refer. 



The details thus given make it plain that we cannot have recourse to the 

 lake theory, for the terraces are not horizontal, but slope with the valley, and 

 in the case of both rivers we reach a point below which any barrage is incon- 

 ceivable, and yet these deposits hold on their course. 



But there are certain additional circumstances to which I ask attention, and 

 which I was led to notice only as the result of having continuously examined 

 the whole course of these rivers. 



Sketch 14. — Kildean on the Forth. 



First, there is the difference between the upper Earn and its feeder, the 

 Ruchil. There are three streams which meet at Comrie, where the Earn, 

 coming straight from its loch, is joined by the Lednoch from the north, and the 

 Ruchil from Glenartney in the south. Both these feeders show the terraces, 

 those on the Ruchil being, as we have seen, specially remarkable. On search- 

 ing for them along the upper Earn I was struck by the difference. The present 

 banks of the stream are unusually low, and above these there is a second 

 terrace, some 12 or 14 feet over the river ; and this was all I could make out. 

 Some banks which I took for the highest terrace I found were due to the rock 

 structure of the country, and some gravel deposits near Aberuchil belonged 

 evidently not to the Earn, but to a mountain stream which comes from the 

 south. The general appearance of these low terraces along this part of the 

 river will be seen from sketch 15, which the reader is requested to compare 

 with sketch 2, when the difference of scale will be obvious. The threefold 



