Vol. 65.] GLACIAL EROSION IN NORTH WALES. 293 



ornamented by outcropping ledges ; the ridges must have been 

 separated by fully mature valleys drained by perfectly graded, 

 normally branching streams. Some time after the late Tertiary 

 uplift, just before glaciers were formed upon the higher-standing 

 monadnoeks, the valleys previously eroded among them had pre- 

 sumably been somewhat deepened; but, if one may reason from the 

 case of Dartmoor, the general aspect of the "Welsh monadnocks 

 must still have been that of subdued mountains, with dome-like 

 summits and rounded spurs, drained by prevailingly graded streams 

 of accordant levels at their junctions. Some of the larger streams 

 of Wales may have been impelled to incise narrow gorges rather 

 sharply in their former valley-floors, and thus in a very small way 

 the valleys of the smaller side-streams may have come to hangover 

 the narrow gorges cut down by the large streams. But, in the 

 Snowdon area, there are no large trunk-rivers ; all the streams are 

 branching headwaters, and the disparity of volume among them is 

 not sufficient to have produced striking cases of discordant junctions. 

 The features of pre-Glacial Snowdon, as sketched in the opening 

 paragraph of this essay, are thus justified. It would be against all 

 reasonable analogy to believe that the sharp ridges, the steep cliffs, 

 the valley-head cwms, and the valley-floor steps and basins of to- 

 day couFd have existed at that time. 



Nevertheless, if this restoration of pre-Glacial Snowdon were 

 supported only by such inferences as have been here presented, its 

 acceptance might not be confidently urged ; but, fortunately, there 

 are numerous rounded mountains- — moels — in the Snowdon district, 

 which are high enough not to have been overridden, like Moel 

 Trefan, by ice from the north, and which to all appearance were 

 never overwhelmed by the ice of the W T elsh glaciers. These round- 

 shouldered masses undoubtedly suffered some loss of size by the 

 action of weathering, above the level of ice-work, during the Glacial 

 Period ; but this would not significantly change their form. Thup. 

 understood, the moels so well confirm the expectations of the theory 

 set forth above, as to the summit-forms of the pre-Glacial monad- 

 nocks of the Snowdon district, that it seems reasonable to accept 

 the expectations of theory as to pre-Glacial valley forms also. 



XI. Subdued Mountains oe Normal Erosion. 



In order to acquire a vivid impression of the essential character- 

 istics of normal subdued mountains with their domed summits, 

 rounded spurs, and graded valleys, it is desirable to see actual 

 examples of such forms, as well as to discuss the theory of their 

 origin. For this purpose, a visit to the well-worn Appalachian 

 mountains of North Carolina may be commended. There the long 

 continuance of normal subaerial erosion, uninterrupted by glacia- 

 tion, has reduced a great mass of deformed and resistant crystalline 

 rocks to a late mature stage of well-rounded domes and spurs, 

 possessing a local relief of from 2000 to 4000 feet, covered nearly 



Q. J. G. S. No. 259. i 



