ROCK-WEATHERING IN CHURCHYARDS. 66^ 



in our churchyards, where sandstones of this character have been used 

 for pilasters and ornamental Avork, and where the stone set on its edge 

 has peeled off in successive layers. In flagstones, which are merely 

 thinly-bedded sandstones, this minuter lamination is fatal to durability. 

 These stones, from the large size in which slabs of them can be ob- 

 tained and from the ease with which they can be worked, form a tempt- 

 ing material for monumental inscriptions. The melancholy result of 

 trusting to their permanence is strikingly shown by a tombstone at the 

 end of the South Burying Ground in Greyfriars Churchyard. The 

 date inscribed on it is 1841, and the lettering that remains is as sharp as 

 if cut only recently. The stone weathers very little by surface disin- 

 tegration. It is a laminated flagstone set on edge, and large portions 

 have scaled off, leaving a rough, raw surface where the inscription once 

 ran. In this instance a thickness of about one third of an inch has 

 been removed in forty years. 



In the third place, where a sandstone contains concretionary masses 

 of different composition or texture from the main portion of the stone, 

 these are apt to weather at a different rate. Sometimes they resist de- 

 struction better than the surrounding sandstone, so as to be left as 

 prominent excrescences. More commonly they present less resistance, 

 and are therefore hollowed out into irregular and often exceedingly 

 fantastic shapes. Examples of this kind of weathering abound in our 

 neighborhood. Perhaps the most curious to which a date can be as- 

 signed are to be found in the two sandstone pillars which until recently 

 flanked the tomb of Principal Carstares in Greyfriars Churchyard. 

 They were erected some time after the year 1715. Each of them is 

 formed of a single block of stone about eight feet long. Exposure to 

 the air for about one hundred and fifty years has allowed the original 

 differences of texture or composition to make their influence apparent. 

 Each is hollowed out for almost its entire length on the exposed side 

 into a trough four to six inches deep and six to eight inches broad. 

 As they lean against the wall beneath the new pillars which have sup- 

 planted them, they suggest some rude form of canoe rather than por- 

 tions of a sepulchral monument. 



Where concretions are of a pyritous kind, their decomposition gives 

 rise to sulphuric acid, some of which combines with the iron and gives 

 rise to dark stains upon the corroded surface of the stone. Some of the 

 sandstones of this district, full of such impurities, ought never to be 

 employed for architectural purposes. Every block of stone in which 

 they occur should be unhesitatingly condemned. Want of attention 

 to this obvious rule has led to the unsightly disfigurement of public 

 buildings. 



III. Granites, In Professor Pfaff's experiments, to which I have 

 already referred, he employed plates of syenite and granite, both rough- 

 and polished. He found that they had all lost slightly in weight at the 

 end of a year. The annual rate of loss was estimated by him as equal 



