BEISTOL BUILDING STONES. 105 



dry rock woighinc^ about 126 pounds. Subjected to crushing 

 stress, the cubic inch yields without previous fracture to a 

 load of about 1'2 tons, or 3'6 tons to the two-inch cube. The 

 absorptive power is about eleven pints to tho cubic foot, or 

 18'8 per cent, by volume. 



I have made some experiments with cubes and prisms of 

 this rock to tost the effect of alternate freezing and thawing. 

 The result was in each case loss of weight due to tho dis- 

 lodgment of particles from the surface. The loss was how- 

 ever loss uniform than in the case of Old Eed Sandstone, 

 tho surface becoming markedly pitted. 



How mai'ked an effect frost has upon such soft, absorbent 

 oolitic rock may be seen after any winter in Bristol, where 

 the coping stones are but too apt to crumble to powder. 

 The pitted suiface may be also seen in a window frame, 

 where, after a few year's, the diifcrence between the inner 

 and outer aspect becomes sufficiently well marked. The 

 Dnndry stone pits deeper and more iri'cguliirly than the I?atli 

 stone, while in the IDoulting stone the shelly structure is 

 brought out by the process. Where a vein of spar passes 

 through such a rock, the difEerential effect is readily observ- 

 able. Tho general surface being lowered by tho removal of 

 grains, tho vein of spar stands out in relief. See, for 

 example, the coping stones for tho railings round Victoria 

 Rooms, Clifton. In many places in Clifton the numbers or 

 names of houses on the pillars having been protected by a 

 coat of paint now stand out in relief. The action is partly 

 mechanical by the removal of grains, partly chemical 

 through tho action of dissolved carbonic anhydride. If we 

 examine tho exterior of old Bristol Cathedral, however, we 

 shall see that the blocks of Old Red Sandstone have yielded 

 to the disintegrating action of frost and weather (purely 

 mechanical in this case), far more than the surrounding 



