Z GEOIiOOY OF 'I'llK AVON BASJN. 



W. of St. George's, Easton. Jn tlic pi-o.sont contribution I 

 propose to consider the country somcwliat f'artlicr west, in 

 tlio district of Portbury and Clapton. 



Headers of my former paper will I'emcmbor that N. of tlio 

 limestone ridge of Leig'h Downs, tlicro runs a depression in 

 the softer Lower Liniostouo Shales, which, with the slopes 

 of the adjoining limestone, is tlie collecting ground of the 

 head waters of the' Somersetshire tributaries of the Avon. 

 Those tributaries cat notch-like ravines in the Failands ridge 

 of hard conglomeratic Old Red Sandstone, and these them- 

 selves I'eceive minor tributaries in the more open countiy, 

 duo to the incoming of the softer sandy beds of the Ohl 

 Red Sandstone, after which they again enter small gorges of 

 greater or less length, cut in the liai'der and more resisting 

 Dolomitic Conglomerate, on emerging from which they fall 

 into the Avon, or (in the case of the Easton brook) enter on 

 alluvial ground. The general conclusion arrived at was 

 that the Failands ridge and the rising ground occupied by 

 the Dolomitic Conglomerate are outstanding features which 

 have resisted the sandpaper action of the general or snpei'- 

 ficial denudation of rain and frost, but which have been cut 

 into by the file-like action of the special or linear denudation 

 of the streams. For it is as charactoi'istic of general denuda- 

 tion, tliat it acts un(!(]ually on I'ocks of different jiowers of 

 resistance, as it is characteristic of linear denudation that 

 its stream-cut notch is as deep in hard as in soft rocks, since 

 for a river to cut deeper into the softer than into the harder 

 strata would nocessitatu its running uphill to get over the 

 harder ridge. 



2. — The Thysical Features of the District. 

 On the southern border of the area we are now to consitlor 

 runs the elevated ridge which joins Clevcdon and Clifton. 



