108 



BRISTOL BUILDING STONES. 



protective glaze on the rock. When once this protective 

 glaze is removed, the durability of the stone is lessened. 

 Hence the disastrous effects sometimes brought aboat by 

 scraping a building constructed of weathered oolitic stones. 

 Thus the durability of a stone cut to size in the quarry 

 while the quarry water is still retained by the porous 

 material, and then allowed to weather in the quarry, is far- 

 greater than that of a stone removed green, or in any way 

 worked after it has lost its sap. Wren is said to have used 

 no stone in the building of St. Paul's Cathedral that had not 

 weathered for some years in the quarry. And in oolitic 

 quarries may now bo seen carved blocks undergoing this 

 process, and not to be subsequently touched by the tool. 



The walls of houses built of any form of limestone are 

 apt to " sweat." To an inquiry I put to Mr. IJroclc, whether 

 it is usual in this neighbourhood to use brick linings to linu!- 

 stone-built houses, he replies : " In all good houses, when 

 built with limestone of any sort, the inner faces are lined 

 with brick, to prevent moisture running down the walls 

 during change of weather or after frosts. If the whole of 

 the interior atmosphere is kept at 60°, this is in great 

 measure avoided. Great complaints are made in Bath, where 

 the houses are built of oolite, of the ' sweating ' of the walls, 

 which should also be brick lined." 



Ham Hill stone, from the Midford Sands series at the base 

 of the Inferior Oolite, is occasionally used in Bristol. It may 

 be seen in the pillars, etc., of the Colston Hall, and in the 

 lioman Catholic pro-cathedral. It is regarded as one of the 

 best building stones in the West of England. 



Of other stones of this (limestone) class little need be 

 said. Magnesian limestone, used in London with such 

 marked success in the Jcrmyn Street Museum, and with 

 such conspicuous failure in the now Houses of Parliament, 



