BBISTOL BUILDING STONES. 



103 



Mountain LimeHuone, wliich is extensively quarried in the 

 immediate neighbonrhood, at Soutli Mead, near "Westbury- 

 on-Trym, and at Wick, is chiefly used for rough walling. 

 It is an expensive stone to v^rork, being full of joints, which 

 perhaps break when the mason has almost finished the 

 working. When used it is found to be a very durable stone, 

 and good examples may be seen in the boundary wall of the 

 old city Gaol, and the front of the Weighbridge House near 

 the Totterdown Lock. Stones of Mountain Limestone have 

 been built in to the older pai-ts of Westbury Church ; and at 

 the west end of the south aisle an old and narrow doorway 

 has been filled in with this stone. It is occasionally used in 

 houses, as in those in Leigh Woods. Mr. Bastow informs me 

 that where this material is used, a 4|-inch brick lining, with 

 a space between this and the limestone, should always be 

 used. The stone has stood well in Chepstow Castle, though 

 it was employed, I believe, only in the later work. 



The stone varies from a coarse-grained, shelly, crinoidal, 

 or coi'alline rock, with a markedly crystalline fracture, to a 

 close-grained oolite of a very uniform texture. The latter 

 is better in constriiotion. Its specific gravity is 2-7, the cubic 

 foot of dry rock weighing nearly 1G8 pounds. Subjected to 

 crushing stress, a prism two inches square and three inches 

 high, out from Black Rock Limestone (containing -0126 per 

 cent, carbon, and 3'3 per cent, silica), began to crack at 19 

 tons, and broke down under a load of 19-46 tons. A coarse, 

 shelly limestone, containing Spirifers, from near the base of 

 the series showed signs of yielding at from seven to eight 

 tons on the two-inch cube, and broke down when the load 

 reached about twelve tons. The absorptive power is remark- 

 ably low, being often less than one-tenth, and rarely moi'c 

 than four-tenths, of a pint to the cubic foot, or from '2 to '4 

 per cent, by volume. 



