MINERALOGY OF THE REDHEAD. 5iS 



sandstone is first raised in the quarry, it is very soft, 

 and is easily cut with the working-tools ; after 

 exposure for a short time to the atmosphere, it 

 becomes a little harder, but is by no means a very 

 durable material for buildings. When exposed 

 in a wall or house, the surface which has beea 

 dressed with the chisel, remains entire until the 

 portion immediately beneath becomes disintegrated, 

 when the external film falls off. After the arti- 

 ficial surface has been removed, the particles 

 crumble down in succession as they separate from 

 the mass. Is it the pressure of the chisel in the 

 dressing of the stone, which, bringing the par- 

 ticles at the surface into closer contact, enables 

 them to resist longer the influence of the atmo- 

 sphere ? Would it not be advisable to beat the 

 surface of the stones with a hammer, before using 

 them in building, in order to communicate the re- 

 quisite durability ? The Old Abbey of Aberbro- 

 thick is constructed of this kind of rock, and the 

 mouldering surfaces of the stones make the, ve- 

 nerable ruins appear still more ruinous 



In several places, the rock is composed of blunt 

 angular pieces of sandstone, imbedded in a basis 

 of a similar composition. This structure does not 

 appear to the eye, unless the stone has been ex- 



* There was a considerable quantity of fibrous gypsum found 

 some time ago among the rubbish of this abbey. It may have 

 been found in the sandstone-rocks of the neighbourhood^ but of 

 this no proof exists at present. 



