300 PROE. W. MORRIS DAVIS ON [Aug. 1909, 



Needless to say that such features are entirely wanting in subdued 

 mountains of normal erosion. Again, in more or less close associa- 

 tion with the rock-steps in the floors of maturely open valleys in 

 the Snowdon district, is the occurrence of rock-cliffs in the basal 

 slopes of the valley sides. This is all the more abnormal from the 

 fact that the valleys are wide-floored ; for, as such, their sides 

 ought to be weathered back to a moderate declivity. The basal 

 cliffs are not due to the undermining of a resistant stratum by a 

 weaker stratum, such as may often occur in normally eroded mature 

 valleys in districts of horizontal structure ; for the cliffs are often 

 in the same land of rock as that in which the open valley itself is 

 excavated, and in which the higher slopes above the cliffs have been 

 weathered to grade. The steps in valley-floors and the cliffs in 

 valley-walls in the Snowdon district are, indeed, not within reach 

 of explanation by the ordinary processes of erosion. Again, in the 

 immediate neighbourhood of smoothly graded waste-covered rock- 

 slopes, the same kinds of rock may appear in very irregular bare 

 ledges, giving the surface a highly characteristic knobby or craggy 

 form, very suggestive of the recent action of a vigorous eroding 

 agent (see fig. 31, p. 337). 



Indeed, one may say that the general effect produced by an 

 inspection of the Snowdon district is comparable to that caused on 

 looking at a battered and weather-beaten statue : one may imagine 

 that the statue has been at one time ' normally ' carved by a 

 sculptor, for certain parts of the original form may still be pre- 

 served and the rest may be reasonably inferred; but one must see 

 also that, since its carving, it has been exposed to very different 

 treatment, under which it has been more or less defaced. In such 

 a case it may be possible, by restoring the proper form of the lo^t 

 features, to estimate how severely the carved, surface has been 

 battered by rough treatment and pitted by the weather ; and a 

 similar possibility seems to be open in the case of Snowdon. 



XY. Abnormal Forms and Normal Processes. 



It may be fairly presumed that the intensity of the impression 

 made upon the observer by what are here called the abnormal forms 

 of the Snowdon district, will increase with the confidence that he 

 feels in the correctness of the general theory of normal erosion, and 

 with the strength of his conviction that a systematic distribution 

 and succession of hill-and-valley forms must be produced during 

 the progress of an uninterrupted normal cycle. The intensity of 

 the impression will be all the more strengthened if the observer has 

 gained an acquaintance with the forms of normally carved, non- 

 glaciated mountains in various stages of erosion, but particularly in 

 the late-mature stage of subdued form with which we are here 

 most concerned, before he sees any glaciated mountains; for, in such 

 a case, the abnormal features of the latter will produce something 

 of a shock when they are first encountered. A good illustration of 



