106 



BRISTOL BUILDING STONES. 



Oolite or the yellowish Triassic stones. Mr. Ansted tells ns 

 that " the infiuenco of frost on a stone is in proportion to 

 the water it takes up, and determines its dxirability." This 

 statement needs qualification, for the durability is largely 

 dependent on the readiness with which the particles of the 

 rock are dislodged by the superficial action of frost, which, 

 in my experiments, is greater in Old Red Sandstone than in 

 Dundry stone, though the absorbent power of the Dundry 

 stone is the gj'eater. 



The rate at which a stone disintegrates from tlic action of 

 frost is determined very largely by the aspect of the exposure. 

 Stones in those parts of a building which have a southerly 

 or south-westerly aspect are apt to disintegrate far more 

 rapidly than those with a northerly or north-easterly aspect. 

 This is in the main due to the fa,ct that during the winter 

 south and south-west walls receive the sunshine of the day 

 after the frost of night, whereas north and north-east walls 

 may remain fr-ozon for weeks a,t a time, it is not either the 

 long continuance or the intensity of frost that (lisintegr.'ites 

 the rock ; it is the alternation of frost and thaw. 



In my experiments on Dundry stone 1 did not find that 

 the alternate freezing and thawing appreciably altei'ed the 

 resistance to crushing stress. Nor did (1) altei'nate heating 

 and cooling, or (2) alternate soaking and drying produce 

 any weakening efl'ect. All such actions have mei'ctly a, 

 superficial effect. Disintegration is a matter of the surface. 



Donlting stone is from the Inferior Oolite near Shopton 

 Mallet. It is a shelly .Jura-ssic; Limestone, very hard and 

 durable. It has been used in the construction of Wells 

 Cathedral and Glastonbury Abbey, and was the material 

 selected by Mr. Street for use in the restoration of Bristol 

 Cathedral. It is a heavier stono and a more compact than 

 Dundry, the specific gi'avity being .about 2'('), and the cubic 

 foot weighing some 130 pounds. 



