THE AGE OF THE WYE. 
183 
backj on an average, about five-eights of an inch in the 200 years. 
It is to be noticed, however, that there is a variety in this respect, 
for that some of the beds of stone are better than others and do 
not fall into decay so fast ; but all the old red beds in this district 
are subject to it, with the notable exception of one great bed, 
presently to be alluded to, which occurs on the higher ground sur- 
rounding the Forest of Dean. 
Another and most remarkable fact, connected with this 
subject, is that, in this neighbourhood, there is no good building 
stone to be got near the surface of the ground. In making the 
deeper railway cuttings, beds of capital building stone were found 
at a depth of twenty feet or more below the surface ; but none 
nearer the top. A 3-feet bed of firm building stone, for instance, 
may be followed for many yards along the deeper part of the 
cutting, where it is hard and strong, but, as this same bed rises 
towards the surface, it gradually gets softer until, when only 8 or 
1 0 feet under the soil, it becomes what is locally called “ dun- 
stone,” a sort of indurated sand in the form of rock, but which 
can be broken easily between the fingers. Every bed of rock in 
the cutting may thus be followed to its outcrop, being hard rock 
when 20 feet or more below the surface, and dunstone when only 
8 or 10 feet below. This “ surface softening ” of the beds of 
rock is no doubt due to the same weathering process, already 
alluded to, continued through a vast period of time. It is quite 
general and is characteristic of the material. All the rock is 
“ dunstone” within 10 feet of the surface, and no “ dunstone” 
is ever found at a depth of 20 or 30 feet below. There are, 
occasionally, beds of marl amongst the rock beds. Where these 
crop out the beds of rock beneath the marl are somewhat less 
softened than usual ; as if the atmospheric influences could not 
get through marl so easily as through rock. 
The disintegration of the rock, in the case of this surface 
