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in the original direction at some 

 height above its present course is 

 suggestive of capture by a stream 

 with greater corrosive power, 

 possibly due to the Bwlch-vr- 



Hwch Fault. The Himant con- 

 tinues to run as a strike stream 

 again as far as Aber Hirnant, 

 where it makes another bend ; 

 and the lower part of its course 

 is clearly controlled by the stmc- 

 ture of the country. 



III. The Ge>t:eai. 

 Succession. 



The rock-succession here de- 

 scribed comprises pre-eminently 

 a series of shallow-water depo- 

 sits : even the black Xant-hir 

 Shales appear to be current- 

 bedded, and to this we may per- 

 haps ascribe their unfossiliferous 

 nature. The JSandy Mudstones 

 contain bands and even whole 

 beds ripple-marked and to some 

 extent also current-bedded, while 

 the oolitic nature of the Gelli- 

 Grrin Liuiestone at T Garnedd 

 points in the same direction. 



The succession is interesting, 

 mainly on account of the 

 development of the ashes and 

 lim estones. The ash- beds, of 

 which there are tvro in all, belong 

 to the Caradocian : both die out 

 southwards, although, the lower 

 is the more persistent, and both 

 serve admii-ably to bring out the 

 structure of the country. The 

 limestones are remarkably im- 

 persistent, and occur more or 

 less spoi-adically throughout the 

 series ; they have little or no 

 value as stratigraphical units. ^ 



^ Some places mentioiied. in the fol- 

 lowing pages lie outside the area of 

 the accompanyiiig map (PL ID. but 

 thev may be fotuid. on the 1-inch 

 Ordnance Map and on the 1-inch Greo- 

 logical Map, Sheets 74 N.TV. i S.W. 



