182 
THE AGE OF THE WYE. 
this evidence it may also be added, on the other hand, that if 
sufficient time is allowed, the forces of the river are quite 
sufficient to account for the whole of the facts. 
My purpose now is to deduce from these facts, so nearly ae 
I can from such observations as I have been able to make, the 
length of time that would he required for the river to do what 
we see it has done, supposing the natural forces to have been the 
same as we now find them. 
The old red sandstone of this district, though much used for 
building purposes, is not a good weather stone. A house built 
of it keeps its face pretty well for about 20 years ; the surface 
of the stone then begins, very gradually, to peel off, the tooled 
surface having the appearance of, for a time, preserving the face 
of the stone, which then peels off in a flake. The exposed face, 
afterwards, slowly assumes a rounded and sandy appearance ; as 
may be observed in all old buildings made of this material. 
To j udge from its appearance, I should fancy that the grains 
of sand forming the material of the stone were held together 
by a cement of iron, and that by exposure to the air, the iron 
became gradually oxidised and lost its hold, the particles of 
sand being then washed away by the rain. The process is, no 
doubt, a very slow one, but it is constant ; for the older the- 
building the greater is the evidence of wear, more particularly in 
projecting stones. In Hereford Cathedral, for example, all 
the salient ornaments have been washed off ; and though the face 
of the work has since been restored, at great cost, it w^as with the 
same sort of stone, and this is again beginning to go in the same 
way. The old Market-house in Boss is another good example. 
It w’as built during the reign of Charles the Second, or 200 years 
ago, and the stones have acquired that rounded and sandy 
appearance already alluded to. From the best measurement I 
could make, I ascertained that the face of the work had worn 
