THE LAKES OF SNOWDONIA AND EASTERN CARNARVONSHIRE. 459 



way in which they have resisted the agents of denudation, that the country now presents 

 such a rugged and wild aspect. The principal orographical features of the district had 

 been determined before the advent of the Ice Age. A sufficient interval of time had 

 already elapsed for the ordinary agents of denudation to carve out the valleys and to 

 sculpture the rocks into something like their present diversified forms before the glaciers 

 began to do their work. All the main valleys are, therefore, pre-glacial, and have merely 

 been modified by subsequent events. 



The signs of glaciation which abound in this district have been very fully described 

 and interpreted in the works of Sir Andrew Ramsay, and so are well known to all 

 geologists. The Snowdonian mountains were the nurseries of great glaciers, which crept 

 down the valleys on to the low grounds. The ice-streams flowing down Nant Francon, 

 the Pass of Llanberis, the Gwyrfai Valley, and the Nantlle Valley, became confluent on 

 the low grounds which lie between the mountains and the Menai Straits, and were met 

 there by the vast ice-sheet which, coming from the north, overwhelmed Anglesey, and 

 skirted the North Wales coast to pass on towards Cardigan Bay. On the other side of 

 Snowdon a huge glacier moved down the Vale of Gwynant towards Beddgelert and 

 Aberglaslyn, and another passed eastwards along Nant-y-Gwrhyd to Capel Curig, where 

 it was met by a glacier coming down Nant-y-Benglog, the united stream then continuing 

 its course towards Bettws-y-Coed. 



The striae which can be seen on the rock surfaces always trend in the directions in 

 which these main valleys run. The main streams were joined by tributary streams 

 coming down from the cwms and upland valleys. The highest peak of Snowdon — 

 Y Wyddfa — formed a centre from which radiated six glaciers, which made their way 

 down to join the ice-streams in the bigger valleys below. The Nant Francon glacier was 

 augmented by tributary glaciers coming down from a number of cwms which overhang 

 the main valley on the left, and lower down was joined on the opposite side by the 

 bigger tributary streams of Cwm Llafar and Afon-Gaseg, which emerged from the north- 

 western flanks of the Carneddau and Y Foel Fras. South of Nant Francon, at the head of 

 Nant-y-Benglog, a few cwms also occur on both sides, and from these tributary streams 

 moved to join the mass of ice creeping towards Capel Curig ; some of the ice moving in 

 this direction was probably diverged over the low col above Llyn Cawlyd into the valley 

 where the lake now lies. The mountainous country lying to the north-east of Capel Curig 

 also gave birth to glaciers which moved north-eastwards towards the Vale of Conway. 



Thus, at a certain period, every valley was filled by its own special glacier, those in 

 the cwms and upland valleys going to feed those in the bigger valleys, and these again 

 moving outwards in all directions from the mountains to spread out as fans over the 

 lowlands. The track of the old glaciers is marked at many places by smoothed, 

 rounded and striated rocks, the strise indicating the direction of the ice-flow. The 

 cwms are especially rich in the remains of glacial action, and huge moraines are there 

 seen in all stages of preservation. These mark the final retreat of the glaciers after the 

 ice had disappeared from the low grounds. 



TRANS. ROY. SOC. EDIN., VOL. XL. PART II. (NO. 20). 3 z 



