Philip LaJce—Bala Lake and Riccr Si/ston. 213 



valley is indicated by a heavy line. Some of the faults are continued, 

 m then- probable directions, into the area which is now concealed 



' by drift and alluvium ; and an additional fault (N) is inserted which 

 IS not shown upon the geological map. The existence of this is 

 somewhat doubtful, but the foot of the hills is here so extraordinarily 



' straight that I cannot help suspecting that it coincides with a line 

 oi fault. 



A comparison of this diagram with the topographical map (Fig. 5) 

 will show that the actual contour of the ground agrees very closely 

 with the contour which would be produced by the faults, if it were 

 determined by them alone. It is true that a few of the faults, such 

 as that near Drws-y-nant-uchaf, have no effect upon the surface. 



\-„j5' 



Fig. 5.— Sketch-map of the topography of the vaUey of the Bahi Fault 

 near the watershed. 



But generally each fault is marked by a more or less sudden change 

 of slope, and the ground on the downthrow side of the fault lies 

 lower than that on the upthrow side. This is sometimes well shown 

 even where the rock is similar in character on both sides of the 

 fault. Attention may be drawn, for example, to the fault west of 

 Pant-gwyn. 



