Philip Lake — Bala Lake and Rivev System. 245 



tributaries of the Clwyd ; the Conway itself; and the rivers of 

 Snowdonia, which occupy Nant Ffrancon, the Vale of Llanberis, and 

 the valley of Llyn Cwellyn. I am not, however, in a position to 

 discuss this question more fully, nor am I prepared to assert that 

 all these streams belong to the same radial system. 



There is certainly one important river which seems to be exceptional, 

 namely, the river which flows through the pass of Aberglaslyn. 



But the broad outlines of the river history of North Wales seem 

 to be clear. A radial system of drainage was established ; and 

 subsequently a series of transverse valleys was formed, which broke 

 up the radial system into sections, and each of the main transverse 

 valleys carries away the drainage of one or other of these sections. 



The transverse valleys were, I believe, formed by faults, with 

 an upheaval on one side ; but further investigation is needed to 

 elucidate this point. One of the faults appears to have assumed for 

 some distance the character of a trough, with the consequent 

 formation of a lake, which is now Bala Lake ; and it seems that the 

 development of this trough was subsequent to the original formation 

 of the valley. 



If it were not for these transverse valleys, the drainage system 

 of North Wales would be very similar to that of the Lake District, 

 and the Vale of Clwyd would be the analogue of the Vale of Eden 

 in Cumberland. 



Summanj. 



In the foregoing pages I have endeavoured to throw some light 

 upon the formation of Bala Lake and to sketch the development 

 of the present somewhat complicated river system of North Wales. 

 The explanation suggested is simple and fairly consistent ; but it 

 is still, in many respects, hypothetical. This is especially the case, 

 perhaps, with regard to the share attributed to the faults, in the 

 production of the present topography of the country. On this and 

 many other points, further research is certainly necessary. Yet 

 from the evidence adduced, it seems that the following conclusions 

 may, with some probability, be drawn : — 



1. Bala Lake belongs to the same valley as the River Wnion ; and 

 the drainage of this valley formerly flowed into the sea near Barmouth. 



2. Bala Lake and the rest of the valley as far to the south-west 

 as Pant-gwyn lie in a trough between two faults, modified by other 

 faults crossing the trough obliquely. 



3. The position of the watershed in this and in several other 

 similar valleys has been determined by earth-movements. 



4. The original drainage system of North Wales was a radial 

 system, the centre of which lay in the high ground around the 

 sources of the Conway. Subsequently a series of transverse valleys 

 was formed which divided the radial system into sections, and 

 each of the principal transverse valleys now carries away the 

 drainage of one of these sections. Bala Lake was formed in one 

 of the transverse valleys, probably not at the same time as the valley 

 itself, but at a somewhat later period. 



