VOL. XVII. (i) SOME GLACIAL FEATURES IN WALES 37 



In Plate VIII., fig. i, is a view of the Grimsel Pass, 

 in Switzerland, which shows very clearly indeed the wide- 

 spreading amphitheatral cwm, the glacier-tarns at its foot, and 

 the peculiar broken tooth-like surhmits of the mountain-mass, 

 due to the headward growth of the neve-reservoirs. Therewith 

 compare the lower picture on the same plate, which is a 

 reproduction of a photograph of the eastern part of Snowdon. 

 High up on the slopes of Cader Idris, near Dolgelly, beneath 

 the summit, is a beautiful little glacier-tarn, ponded back by a 

 well-defined moraine, and backed by precipitous cwm-head 

 walls (Plate IX.) 



Now, although there are many features that are attributed 

 to glacial origin which are independent of the rock-structure of 

 the glaciated mountain-mass, it is nevertheless obvious that 

 the pre-Glacial geomorphology of a given mountain-mass of 

 normal-erosion production must have been mainly connected 

 \vith the distribution of relatively hard and soft rocks, faults, 

 anticlines and synclines, etc.. and that the features so pro- 

 duced were developed and sharpened by the forces at work 

 during the Glacial Period. Thus, while in Snowdonia, owing 

 to the rock-structure, geographic position, and altitude, the 

 products of Glacial erosion are numerous and well-defined, 

 in other parts where the mountain-masses are lower, of more 

 uniform and less deformed structure, and were less glaciated, it 

 is apparent that the glacial features also will be less pronounced. 



THE BRECON BEACONS 



Some six miles away from Brecon, in a southerly direction, 

 are the Brecon Beacons (Plate X.) — a residual portion of 

 the great escarpment of the Upper Old Red Sandstone, which, 

 starting as a comparatively ill-defined ridge between May Hill 

 and the Forest of Dean, on the borders of Gloucestershire and 

 Herefordshire, becomes — in spite of several interruptions — 

 more and more pronounced as it passes through the southern 

 portion of the latter county (as the Black Mountains), cul- 

 minates in the sharp-peaked Brecon Beacons, and only com- 

 mences diminishing conspicuously in altitude after it has 

 passed the dark Carmarthen Fans, and has reached the neigh- 

 bourhood of the county-town of Carmarthen. These hills are 



