THE AGE OF THE WYE. 
195 
an exposed bed of the old red rock, the surface of which lay 
15 or 16 feet below the ground and about 7 feet below the 
alluvial level, so that the foundation is exposed to the air when 
the water is at its ordinary level, but is subject to the action of 
the stream on the occurrence of any “ fresh,’’ a position the most 
favourable for wear that I can imagine. Now this bed is by no 
means composed of the best and firmest quality of stone in this 
district, for it is comparatively thin, and what is here called 
“ shelly,” or composed of laminae of less than an inch in thick- 
ness, and it is not more than 16 feet below the original surface; 
but it is certainly a very hard bed considering these circum- 
stances. 
I found, by careful measurement, that the whole surface of 
this bed has, in the course of the 257 years since the bridge was 
founded upon it, been worn away 3f inches — that is, at the rate 
of an inch in 64-|- years. 
This rate of wear is very much faster than that showm by 
the old Market House ; but it must be borne in mind that the 
stone selected for the old building was of a better quality than 
the bed at Wilton Bridge, that the stones were fresh and hard 
out of the quarry, and that it would take many years for the 
atmospheric action to get well into them, and also that the con- 
ditions of river wear must be more severe than that of the 
elements alone. 
We have now got the elements of our calculation — let us 
sum them up. We have ascertained, firstly, that the cliff at 
Boss has been worn back at least 300 yards; secondly, that, 
taking the time from the origin of the river, 110 yards of the 
cliff are under full wear, while an average length of 1073 are 
under half wear ; and, thirdly, that the rate of wear has been an 
inch in 64 1 years. And these figures have been taken at a 
minimum. 
