OF THE EARN AND TEITH. 155 



time the barriers had been lowered, and as the waters fell these terraces are 

 the old lake margins showing the different heights at which the waters once 

 stood* 



One fatal objection which applies equally to this view and to the theory 

 of their marine origin, is that these terraces lie up and down the valley not 

 horizontally, but according as the bed of the stream rises and falls. The 

 parallel roads of Glenroy are an example of how it would have been if they had 

 been formed either by the sea or by the standing waters of a lake. In Glen 

 Roy they lie on a horizontal level, keeping their own height without regard to 

 the bottom of the valley. On the Earn, however, the case is reversed ; the 

 terraces follow the inclination of the river bed ascending as it ascends towards 

 the hills, descending as it descends towards the sea. Take the intermediate 

 terrace, for example, on which lies the Roman Camp south of Comrie. Beginning 

 at a point above Cultibregan we can trace it as it spreads out and goes down 

 to Lennoch three and a half miles below. To the eye it seems to lie on a dead 

 level ; and yet, as shown by the Ordnance Survey, it has a decided incline, 

 being 71 feet higher at Cultibregan than it is at Lennoch, while its height 

 above the river bed is nearly the same. The river course appears to have 

 descended about 68 feet, so that the two have nearly kept pace with each other, 

 and the same thing is found all along the valley. The terraces descend as the 

 river descends from where they leave the hills to where they meet the tide. 



This is of course decisive, but the true nature of these deposits can only be 

 fully understood when one follows them continuously from point to point along 

 the whole river valley. There are localities, it must be confessed, where to an 

 ordinary spectator the theory of lake margins would suggest itself as exceed- 

 ingly probable. Near Strowan, for example, under the hill on which stands 

 the monument to Sir David Baied, the river passes through a gorge, and looking 

 up along its course you see the terrace-like deposits lining the wide open valley 

 on either side, one of them bearing on its surface the church of Monzievaird. 

 Would not one naturally say that the gorge had once been barred and a lake 

 formed, of which these are the old margins ? But the fallacy of this is seen 



* As this paper deals only with, a question of local geology, I do not refer to any writers except 

 those who have treated of the two rivers to which these researches are confined. 



Mr Milne-Home applies this explanation of Lake Margins to the Terraces of the Teith, Trans. 

 Roy. Soc. of Edin., vol. xvi. p. 416, 



Dr Fleming supposes a lake to have occupied these river valleys, Lithol. of Edin. p. 76, 1859. 



I may refer also to a discussion before the Geol. Society of Edin., 19th March 1867, the report 

 of which appeared at the time. Only two theories, the Lacustrine and Marine, found support. 



Mr Charles Nicolson, M.A., B.Sc, read a paper on the Surface Formations of the Tay at Perth, 

 describing the Terraces, and advocating the view that they are of Lacustrine origin. 



The President Dr Page, Mr Coyne, C.E., and others, gave " their opinion on these Terraces in 

 opposition to Mr Nicolson's Lacustrine Theory maintaining their marine origin, Dr Page instancing 

 the minute examination by Dr R. Chambers of the old sea margins, and Mr Coyne giving his 

 opinion from minute measurements and personal observations." 



