aKUtiOOY OK TITH AVON BASIN. 



11 



4. — The Gonncctinn hehveon Scenery and Btruciure. 



Thoro is to my mind no donbt that tlie scenery of the 

 district is the direct product of the action of denudation. 

 The streams, with their file-like action, hn,ve cut down 

 Viilloy-notchos to the same depths in harder and softer 

 rocks ; but tlie general or superficial denudation, due to 

 rain, frost, and weather, which I before likened to the 

 action of sandpaper, has broadened oi.it the valleys and 

 lowered the water-sheds where the strata are soft, and has 

 left the harder materials outstanding as ridges, notched hero 

 and there by the brook-files. 



Taking the Portbury district, the striita stand as follows 

 with regard to their resistance to the action of superficial 

 denudation : — 



Moimtiiin Limestone . 



, resi&tinfj. 



Lower Limestone Sliales 



. yielding. 



Upper Old Red Sandstone . 



. resisting. 



Lower ,, ,, . . 



. yielding. 



Dolomitic Conglomerate 



. resisting. 



Trias Marls 



. yielding. 



And throughout the district the yielding beds ai'e low-lying 

 or occupy depressions, while the more resisting beds stand 

 out as ridges. 



A.S we shall see in the next section, a groat fault separates 

 the Coal Measui-es of tlie Clapton District from the Old Red 

 Sandstone of tlio Portbury district. One might well suppose 

 tliat a fault with a throw of some thousands of feet would 

 have left a well-defined mark on the scenery of the area; 

 but it is not so. A change of scenery is indeed produced ; 

 l>ut this is due to the fact that beds of different power and 

 mode of i-osistanco are introduced. It is a iu)teworthy fact 

 that the exact line of fault between Coal Measures and Old 

 Red Sandstone has to be somewhat arbitrarily filled in on 



