OF THE EARN AND TEITH. 



171 



side of a valley 60 feet above the present bed of the stream, and we are told 

 that the human period must be carried back through the long ages needful for 

 wearing down the rocky floor of the valley. These are, I believe, among the 

 strongest arguments from geology. 



But now, if the analogy of our Scottish rivers may be trusted, there seems 

 fair ground for asking whether such arguments have not been carried too far. 



1. First, it is plain that previously to the time when these high-level terraces 

 were deposited along our river courses, the rocky structure of our Scottish 

 valleys had been hollowed out as deep as they are now. In proof of this, it is 

 enough to refer to the fact that the boulder-clay which belongs to an ante- 

 cedent period is found occasionally forming the floor of the valley over which 

 the streams flow."" If, then, the formation of the valleys of France and Devon- 

 shire were analogous to ours in Scotland, their rocky structure was excavated 

 not after, but before, the dej)osition of the high-level gravels. 



2. Secondly, The floods which piled up these old high-level deposits seem to 

 have had the power of doing so at a time when the river-bed was cleared of 

 all other materials, and stood at as low a level as the present streams. 



This might be shown by various examples along the Earn ; but we take a 



Sketch 18.— Below the Castle of Monzie, 1866. 



single case from the valley of Monzie. Sketch 18 shows a spot where the 

 stream has cut into the highest terrace,t laying it open from the base up to a 

 height of 50 feet, and showing that it is composed of stratified gravels, sands, 



* Seen in the valley of the Turrit, for example, above Crieff, and also in that of Monzie, in both of 

 which it underlies the high-level gravels. My attention has been called to the fact that this view had 

 been brought forward in the Memoirs of the Government Survey on Berwickshire, p. 50. 1863. 



I" This forms a continuation of terrace c shown in Sketch 4 on the left bank of the stream. It 

 lies a short way further up the valley. 



