TRANSACTIONS OF SECTION C. 763 



12. Glacial Notes at. Rhyd-ddu, Carnarvon. 

 By J. R. Dakyns, M.A. 



Terminal Curvature. 



Near Rhyd-ddu g'lacial striae are to be seen at the following places, to wit : 

 near the railway station, at ahoiit 627 feet above the sea, running N. 30° W. ; near 

 Rhos-clogwyn slate quarry, at 900 feet, running N. 50° W. ; and near the path to 

 Snowdon at 1,200 feet above sea level, running N. 50° W. These strise indicate a 

 general motion of ice down the valley of the Garfai in which Llyn Owellyn lies. 



On the west side of Llyu-y-Gader (out of which the Garfai flows), not much 

 above the level of the lake, there is an old slate quarry in ground sloping gently 

 to the north-east, in which the planes of slaty cleavage, strilsing north-east and 

 dipping north-west, have their weathered edges bent over towards the north-west. 

 As this coincides with the direction of ice-flow indicated by the strife mentioned 

 above, it is but natural to suppose that the bending over was caused by the ice 

 moving towards the north-west. 



But at quarries in the neighbourhood the cleavage planes have not been bent over ; 

 they have not been so attected at the llhos-clogwyn quany, near which strife 

 were observed, nor at the Cwm y Llan quarries ; nor at two other old quarries 

 distant only a hundred yards from that exhibiting the curvature, but on higher 

 ground. 



It is therefore clear that the moving object which bent over the cleavage 

 planes must have been confined to the very bottom of the valley. The observed 

 phenomenon could not have been caused by the glacier, whose striiE are to be seen 

 on the rocks up to at least 1,200 feet above sea level. 



Till. 



In some parts of the basin of the river Colwyn a stratified stony clay exists in 

 ■which the included stones are all lying flat. In one section this till is seen to 

 consist of three perfectly distinct divisions. It seems to me to be obviously of a 

 sedimentary' origin, let down (after the manner suggested by Mr. Goodchild) as a 

 frozen mass of mud, stones, and ice gradually melted. 



WEDNESDAY, SEPTEMBER 12. 



The following Papers and Reports were read : — • 



1. Beach Formation in the Thirlmere Reservoir. 

 By R. D, Oldham, Geological Stirvey of India. 



Readers of Mr. Marr's book on the * Scientific Study of Scenery ' will recall the 

 contrast drawn between the irregular and angular outline of the Thirlmere Lake 

 reservoir, due to the submergence of a land surface shaped by subaerial denudation, 

 as contrasted with the more gracefully curved outline of the natural lakes, where 

 wind, waves, and streams have combined to round ofl'the angulaiities by wearing 

 away the prominences and filling up the re-entering angles. This reproach seems 

 to the author to be somewhat exaggerated, as the shore lines of ihe Cumberland 

 Lakes have only been partially remodelled by wave action and delta formation, 

 and the original outlines due to simple submergence are still to be seen. However 

 this may be, the reproach, such as it is, is in process of removal. All along the 

 shore of the Thirlmere Lake incipient beach erosion is to be seen, and towards the 

 northern end of the lake, where the shores close in and are exposed to the force of 

 the waves driven along the length of the lake by the prevailing southerly winds, 

 typical beaches and beach curves are being developed. Lantern slides showing the 

 as yet incompleted transition from the irregular outlines produced by submergence 



