THE OLD RED SANDSTONE. 187 
cally at least, the degrading process is the same as that to 
which sandstones of a different but equally inferior quality 
are exposed during severe frosts. In the course of years, 
however, this sandstone, when employed in building, loses its 
salt; crust after crust is formed on the surface, and either 
forced off by the crystals underneath, or washed away by the 
rains; and then the stone ceases to waste, and gathers on its 
weathered inequalities a protecting mantle of lichens.* The 
most valuable quarries in the Old Red System of Scotland yet 
discovered, are the flagstone quarries of Caithness and Car- 
mylie. ‘The former have been opened in the middle schists 
of the lower, or Tilestone formation of the system ; the latter, 
as I have had occasion to remark oftener than once, in the 
Cornstone, or middle formation. The quarries of both Car- 
mylie and Caithness employ hundreds of workmen, and their 
flagstones form an article of commerce. ‘The best building- 
stone of the north of Scotland — best both for beauty and 
durability — is a pure Quartzose Sandstone furnished by the 
upper beds of the system. ‘These are extensively quarried 
in Moray, near the village of Burghead, and exported to all 
parts of the kingdom. The famous obelisk of Forres, so 
* When left to time the process is a tedious one, and, ere its accom- 
plishment, the beauty of the masonry is always in some degree de- 
stroyed. The following passage, from a popular work, points out a 
mode by which it might possibly be anticipated, and the waste of sur- 
face prevented : — “ A hall of which the walls were constantly damp. 
though every means were employed to keep them dry, was about to 
be pulled down, when M. Schmithall recommended, as a last resource, 
that the walls should be washed with sulphuric acid, (vitriol.) I¢ 
was done, and the deliquescent salts being decomposed by acid, the 
walls dried, and te hall was afterwards free from dampness.”’ — (Ree- 
reations in Science.) 
