176 



REPORT 1875. 



Bristol. The tidal portion of the river continues its course by a new cliaunel, 

 cut about seventy years ago south of the city, to its junction -with the 

 Severn estuary at Kingroad. The fresh water of the river, impounded by 

 the dam at Netham, is diverted by a canal into the heart of the city, passing 

 under Bristol Bridge through what -was formerly the old course of the river, 

 but now converted into the Bristol floating harbour. Into the harbour 

 enters also another affluent, the Prome (Gloucestershire), taking its rise in 

 the hills above Wickwar and Chipping Sodbuiy. The docks at Bristol have 

 therefore the advantage, in short-water seasons, of the combined volume of 

 these streams, -which, after passing through the harbour, is discharged at the 

 various outlets of the locks and basins. 



The entire drainage-area of the Avon and its tributaries above Netham is 

 about 795 square miles, and that of the Gloucestershii-e Frome about 68 

 square miles, making the total area draining in through Bristol Harbour 

 about 863 square miles. Between Bristol and the mouth of the river the 

 area draining into the Avon is very limited, amounting only to about 31 1 

 square miles, the chief drainage of this jjart of the district being direct into 

 the Severn. 



The longest branch of the Avon, from its rise above Tctbury to Bath city 

 bridge, is, taking its winding course, about 46 miles. The navigable part 

 of the river from Bath to Netham is about 14| miles, and the tidal portion 

 from Netham to the junction with the Severn about 11 miles. Total length 

 about 72 miles. 



The fall in the bed of the Avon from Bath to the Severn is as follows, 

 viz. : — 



Between Bath and Netham Dam there are several weirs for impounding the 

 water for mills and for navigation purposes. 



The very interesting geological features of the district around Bristol will 

 probably be dealt with in some other Section of the present Meeting ; but it 

 may be within^ the scope of this paper just to remark that there are few 

 rivers of the size of the Avon which embrace in their drainage-areas so 

 great a geological range. Every formation from the Old Bed Sandstone to 

 the Upper Greensand and Chalk inclusive will be found within its water- 

 shed._ About two thirds of the whole consists of the various strata of the 

 Oolitic system, while the remaining one third is made up of a small area of 

 Chalk with the Greensand formations on the east, and on the -west chiefly 

 Lias, together with the formations below it down to the Old Bed Sandstone. 



Although there are no mountainous elevations in the drainage-area of the 

 Avon, the greater part of the country is of a hilly character. The general 

 average elevation of the upper part of the watershed may be taken as about 

 300 feet above mean sea-level ; but there will be found many outliers of the 

 great and inferior oolites rising from 600 to 700 feet. The hills of greatest 



