GKOLOGY OF TIIR AVON BASIN. 



So that the Portbnry brook, rising in the KOnthorn ridge 

 (part of that which runs from Clifton to Clevedon), crosses 

 a lino of depression, cuts through a belt of high ground 

 (continuous with the Failands ridge mentioned in my pre- 

 vious paper), enters and flows through the open country S. 

 of Conygar Hill, cuts a notch in the Portbury ridge to the 

 K. of tliat lull, and then escapes into the alluvial flats. 



The streams on either side of it, the Baston brook and the 

 (Charlton brook, differ in that they rise in the second or 

 Kailands ridge, the latter cutting a deep combe in the ridgo. 



The Caswell brook rises near Moat House Farm, in the 

 (Jlifton-Clevedon ridge. It too, like the Portbury brook, 

 soon crosses a line of depression, wliero it receives tribu- 

 taries larger and more important than itself. It then enters 

 liullock's ]3ottom, the beginning of a long stream-cut combe, 

 from which, it emerges near Caswell Cross cottages. In this 

 combe, however, one misses the o[)en space which, in the 

 <'ase of the Portbury brook, sej)arates the upper notch in 

 tlie Pailands ridge fi'om the lower notch in the Portbury 

 I'idge ; for the Failands and Portbury ridges here coalesce. 



'I'o sum up then the features of the Portbury district : 

 'J'o tho S. lies the Clifton-Clovedon 1-idge, in which rise the 

 Portbury and Caswell Brooks ; N. of this is a narrow line of 

 depression ; farther N. is a ridge of irregular width, which 

 is notched by tho Portbury and Caswell Brooks, and in 

 which rise the Easton and Charlton Brooks ; still further K. 

 is tho open valley, over which the Camj) on Conygar Hill 

 keeps guard, and which narrows and ceases to the W., owing 

 to tho coalescence of the two ridges that bound it. Along its 

 northern border is the irregular Portbury ridge, notched by 

 iiH lour brooks ; beyond which again to tho N. is the low 

 ground stretching to the Severn. 



In tho adjoining district of Clapton tlui physical features 



