525 
of Edinburgh, Session 1879-80. 
lime from the dissolved carbonate. Except for the veinings of 
probable sulphate just referred to, the lime, when once dissolved, 
bad apparently been wholly removed in solution. There was further 
to he observed a certain dirtiness, so to speak, which at the first 
glance distinguished the section of crumbled marble from the fresh 
stone. This was due partly to corrosion, hut chiefly to the intro- 
duction of particles of soot and dust, which could he traced among, 
the interstices and cleavage lamellae of the crystalline granules for 
some distance hack from the crust. 
It may he inferred, therefore, that the disintegration of the 
marble is mainly due to the action of carbonic acid in the permeat- 
ing rain-water, whereby the component crystalline granules of the 
stone are partially dissolved and their mutual adhesion is destroyed. 
This process goes on in all exposures and with every variety in the 
thickness of the outer crust. It is distinctly traceable in tombstones 
that have not been erected for more than twenty years. In these, 
which have been standing for a century it is, save in exceptionally 
sheltered positions, so far advanced that a very slight pressure 
suffices to crumble the stone into powder. But with this internal 
disintegration we have to take into consideration the third phase of 
weathering to which I have alluded. In the upright marble slabs it 
is the union of the two kinds of decay which leads to so rapid an 
effacement of the monuments. 
c (3.) Curvature and Fracture.— This most remarkable phase of 
rock-weathering is only to be observed in the slabs of marble which 
have been firmly inserted into a solid framework of sandstone, and 
placed in an erect or horizontal position. It consists in the bulging, 
out of the marble accompanied with a series of fractures. This change 
cannot be explained as mere sagging by gravitation, for it usually 
appears as a swelling up of the centre of the slab, which continues 
until the large blister-like expansion is disrupted. Hor is it by any 
means exceptional ; it occurs, as a rule, on all the older upright 
marble tablets, and is only found to be wanting in those cases where 
the marble has evidently not been fitted tightly into its sandstone 
frame. Wherever there has been little or no room for expansion,; 
protuberance of the marble may be observed. Successive stages 
may be seen from the first gentle uprise to an unsightly swelling of 
the whole stone. This change is accompanied by fracture of the 
