232 THE RIVER-SYSTEM OF NORTH WALES. [May IQOO, 



Palaeozoic period, and later movements some time after the deposition 

 of the Lower Mesozoic formations. A lake-system was regarded by 

 many geologists as indicating a 'youthful' drainage, and it would be 

 interesting to know whether any of the dislocations of Bala Lake 

 had affected the Pleistocene deposits. 



Mr. Salter said that he was much interested in the latter portion 

 of the paper, in which a most instructive and complicated system of 

 river-capture was described. He asked the Author whether he had 

 come across any corroborative evidence, other than the surface-feature 

 noted, such as beds of gravel or other tluviatile accumulations at high 

 levels. The view that considerable earth-movements had probably 

 taken place in recent geological times seemed to the speaker to be 

 quite feasible, and might explain the great height of a very 

 interesting deposit near by, at Moel Tryfaen. 



Mr. Lamplugh asked the Author in what manner he supposed 

 the transverse faults to have taken effect in intercepting and 

 diverting the original radial drainage. 



The Author, in reply, regretted that he had not been sufficiently 

 explicit with regard to the formation of Bala Lake. Although he 

 believed that the waters of the valley in which that lake now lies 

 originally flowed in a south-westerly direction, and although it was 

 impossible, without a boring, to prove that the lake is rock-bound 

 in this direction, yet for reasons stated in the paper he thought that 

 the lake now lies in a rock-basin, the basin having been completed 

 by earth-movements which closed it in on the south-west. He 

 admitted the difficulty of distinguishing between the direct effects 

 produced by faults, and the secondary effects due to difference in 

 hardness of the rocks brought into contact with one another ; but 

 he would point out that the jblique faults which seem to have 

 produced the convex bend in the valley have rocks of similar 

 character on both sides. 



The paper was confessedly speculative, but he could not believe 

 that the coincidence in direction of the numerous streams referred 

 to the original radial system was merely accidental. He was 

 unable to offer any opinion as to the age of the radial system, or of 

 the system of valleys which run from north-east to south-west. 



As to the manner in which the radial system was broken up, he 

 was inclined to believe that movement took place along pre-existing 

 faults which run from north-east to south-west. The ground on 

 the south-east side of each fault was raised across the course of the 

 radial rivers, and in most cases so rapidly that these rivers were 

 unable to keep to their original direction and were deflected along 

 the lines of the faults. 



