INFLUENCES OF TEMPERATURE AND MOISTURE. 145 



any stone but experience of exposure under definite circumstances. 

 The Bath stone, apparently so permanent amongst its native hills, 

 perishes in the salt air of Norfolk ; and few calcareous freestones of 

 any kind will long resist the carbonated and sulphurous atmosphere 

 of London. 



Preserving Power of the Soil. It is worthy of remark that sculp- 

 tured stones buried under ground are perfectly and even wonderfulb 

 preserved, while their fellows left exposed to the sky have almost 

 crumbled to dust. In the course of excavations for the Yorkshire 

 Museum at York, the statues which once stood between the arches of 

 the nave of St. Mary's Abbey were discovered, some with blue, others 

 with red drapery, one with gilded hair, all retaining the most delicate 

 chisel marks. But at a few yards from them, at the west end of the 

 church which they once adorned, the atmospheric influences have 

 nearly obliterated a beautifully sculptured wreath of leaves round the 

 doorway, so that antiquaries have doubted whether they were meant 

 to represent the vine 01 the ivy. 



Waste from Humidity. Frequently, in looking at buildings com- 

 posed of porous materials, like the Portland stone, or a grit freestone, 

 we observe the parts which are overhung by a ledge, and thus kept 

 in a state of continual shade and dampness, to be more rapidly con- 

 sumed than the projections ; but the parts which hasten soonest to 

 decay are those near the ground where they are most affected by rain, 

 and moisture. The same rules are exemplified in many remarkable 

 rocks, as, for instance, in the quartzose conglomerates of the old red 

 sandstone of Monmouthshire and the millstone-grit of Brimham Crags 

 in Yorkshire. The " Buckstone," near Monmouth, is a huge rock 

 inversely conical, expanded above into a large area, but contracted 

 below by continual waste to a narrow base of attachment. This 

 process, a little further continued, might convert the Buckstone, as 

 probably some of the Atones of Brimham have been converted, into a 

 "rocking stone." 



From Changes of Heat and Moisture. In northern zones of the 

 earth the variations of heat and moisture are greatest on the south and 

 west fronts of buildings, and in consequence those fronts to our 

 cathedrals decay most rapidly. This is remarkably the case with the 

 cathedral of York, built of magnesian limestone, which is in many 

 places quite consumed on these fronts, but comparatively uninjured on 

 the northern face. 



The weathering of the surfaces of buildings by the fluctuations of 

 heat and moisture is partly dependent on the structure and composi- 

 tion of the stone. The flagstone of Yorkshire is in many houses at 

 Bradford gradually decayed grain by grain, so that the surfaces of the 

 stone, continually renewed, and never permitting the growth of lichens, 

 appear always neat and clean. The magnesian limestone of the same 

 county, often traversed by veins of calcareous spar, presents frequently 

 a cellular or honeycomb appearance, in consequence of the projection 

 of these veins above the excavated limestone ; but the coarse shelly 

 beds of the Northamptonshire Oolites, and the irregularly laminated 

 VOL. i. K: 



