527 
of Edinburgh , Session 1879-80. 
More advanced stages of curvature and fracture may be noticed 
on many other tombstones in the same burying-place. One of the 
most conspicuous of these has a peculiar interest from the fact that 
it occurs on the tablet erected to the memory of one of the most 
illustrious dead whose dust lies within the precincts of the Grey- 
friars — the great Joseph Black. He died in 1799. In the centre 
of the sumptuous tomb raised over his grave is inserted a large 
upright slab of white marble, which, facing south, is protected from 
the weather partly by heavy overhanging masonry and partly by 
a high stone wall immediately to the west. On this slab a Latin 
inscription records with pious reverence the genius and achievements 
of the discoverer of carbonic acid and latent heat ; and adds, that 
his friends wished to mark his resting-place by the marble whilst 
it should last. Less than eighty years, however, have sufficed to 
render the inscription already partly illegible. The stone, still firmly 
held all round its margin, has bulged out considerably in the centre, 
and on the blister-like expansion has been rent by numerous cracks 
which run, on the whole, in the direction of the length of the stone. 
A further stage of decay is exhibited by a remarkable tomb on the 
west wall of the Greyfriars’ Churchyard (PI. XVI., B). The marble 
slab, bearing a now almost wholly effaced inscription, on which the 
date 1779 can be seen, is still held tightly within its enclosing frame 
of sandstone slabs, which are firmly built into the wall. But it has 
swollen out into a ghastly protuberance in the centre, and is, more- 
over, seamed with rents which strike inwards from the margins. 
In this and in some other examples the marble seems to have 
undergone most change on the top of the swelling, partly from the 
system of fine fissures by which it is broken up, and partly from 
more direct and effective access of rain. Eventually the cohesion 
of the stone at that part is destroyed, and the crumbling marble 
falls out, leaving a hole in the middle of the slab. When this 
takes place disintegration proceeds rapidly. Three years ago. I 
sketched a tomb in this stage on the east wall of Canongate Church- 
yard (PI. XVI., C). In a recent visit to the place I found that the 
whole of the marble had since fallen out. 
The first cause that naturally suggests itself in explanation of the 
remarkable change in the structure of a substance, usually regarded 
as so inelastic, is the action of frost. White statuary marble is 
