214 Philip Lake — Bala Lake and River System. 



It will be observed that several of the most important faults run 

 parallel to the general direction of the valley, some on one side and 

 some on the other, and that in most cases the downthrow of these 

 faults is towards the valley ; the only exceptions are the faults 

 D and E, which indeed are not parallel to the valley, but are nearly 

 so, and are placed symmetrically with regard to it. In these two 

 cases the downthrow is away from the valley. 



There is also a series of transverse or oblique faults, and these 

 throw down either towards Bala Lake or towards the bottom of 

 the valley. 



Except for a wide curve, convex towards the north-west, the 

 whole of the valley north of Pant-gwyn is enclosed between the 

 outermost of the longitudinal faults — the Bala fault (A) on the one 

 hand and the fault B on the other; and both of these throw down 

 towards the centre of the valley. Moreover, the fault B, if pro- 

 duced, coincides precisely (as is very clearly seen in the field from 

 a position near its southern end) with the north-west shore of Bala 

 Lake. The Bala fault is dislocated at several points, but if the 

 northernmost portion be continued in a straight line it will be found 

 to lie nearly parallel to the south-east shore of the lake, but some 

 distance within the water's edge. 



Without any aid from denudation these faults would, of themselves 

 alone, form a valley very similar to that which now exists ; and if 

 we take into account the oblique faults F, M,^ and L and the doubtful 

 fault N, even the convex bend of the valley out of its regular course 

 may be explained as directly due to the faulting. 



The general shape of the valley is, in fact, not unlike that which 

 the faults themselves might be expected to produce. But it must 

 be allowed that the form produced by the faults has been consider- 

 ably modified by subsequent denudation ; and it is difficult, if not 

 impossible, to determine how far the present configuration is to be 

 attributed to the direct efiect of the faults and how far to their 

 influence in guiding denudation. The relation of the faults to the 

 configuration of the ground is, however, so close that they must, 

 either directly or indirectly, be the cause of that configuration. 



Even if we assume that the valley has been actually formed by 

 the faults themselves, it is by no means necessary to suppose that 

 it is so old as, for example, the Bala fault. A comparatively small 

 movement along this fault, perhaps long after its original formation, 

 would be sufficient to account for all the phenomena so far as it is 

 concerned. 



The transverse fault at Pant-gwyn is particularly interesting. 

 Its downthrow is towards the north-east, that is, towards Bala Lake; 

 and it appears to form the southern end of the trough produced 

 by the longitudinal faults. On the north-west bank of the valley the 

 ground is much higher on the upthrow side of the fault than on 

 the downthrow side. But this is not the case on the south-east bank. 

 Yet here, near the bottom of the valley, drift on the downthrow 



' It should be noted that there is no e'S'idence to show which is the downthrow- 

 side of either M or N. 



II 



