SCIENCE- GOSSIP. 



129 



SCENEEY OF LLANBEKLS PASS. 



By F. E. Filer. 



O 



F the many valleys in the Llanberis district, 

 none are richer in indications of past 

 glaciation than Cvvm-Glas. From the great mound 

 at its lower end (illustrated in S.-G. vol. vii. p. 162), 

 heaps of glacial rubbish may be traced far up the 

 valley, the mounds becoming smaller and smaller, 

 until they disappear near two little lakes at an 

 elevation of about 2,300 feet. These lakes, sur- 

 rounded by smoothed and rounded rocks, appear 

 to be lying in two rock basins formed by the long- 

 continued grinding of the ice. Further on, as the 



Cwm, is surrounded by groups of moraine heaps, 

 especially at its lower end ; and on all sides the 

 rocks are mammillated, perched blocks occasionally 

 being left upon their summits. 



A description of the complicated arrangement of 

 the faulted and contorted strata in this district is 

 a work of great difficulty, and is not possible in a 

 short note of this kind. Reference, however, may 

 be made to the volcanic ash which caps the peak 

 of Snowdon, and, sweeping down to Crib Goch, is 

 exposed in fine sections on both sides of the ridge. 



From Plwto] 



Volcanic Strata in Cwm-G-las. 



[by A. W. Denni 



toothed ridge of Crib Goch is approached, the 

 smooth bosses so conspicuous below are replaced 

 by rough and jagged rocks. The change is sudden, 

 as there is no great difference in elevation between 

 the two series, and it suggests the idea that here 

 is the uppermost limit of the glacier, and that the 

 crest of the ridge rose above the surrounding ice. 



In all the valleys lying between the five prin- 

 cipal buttresses of Snowdon there are signs of 

 glaciation, and if after passing the two pools in 

 Cwm-Glas the ridge of Crib Goch is climbed and 

 crossed, a descent can be made into Cwm Dyli. 

 Llyn Llydaw, the largest of the three lakes in the 

 October 1901.— No. 89, Vol. VIII. 



One overlooks Llyn Llydaw, and the other crops 

 out in a steep cliff near the two pools in Cwm- 

 Glas. The weathered face of this cliff shows well- 

 defined strata, composed of felspathic ash, slaggy 

 lava, and interbedded sedimentary layers. A small 

 portion of the strata is shown in the photograph 

 here reproduced. To serve as a scale a piece of 

 paper 3 inches long was pinned in a crevice of the 

 rocks, which can be seen near the centre of the 

 picture. 



From here the ash strikes across the pass in a. 

 N.N.W. direction, and follows the trend of the 

 upland valley, that, bordered on the east by the 

 Published September 25th, 1901. 



