520 Proceedings of the Royal Society 
saccharoid Italian marble. I have also observed a pink Italian 
shell-marble, and a finely f-ossiliferous limestone, containing frag- 
ments of shells, foraminifera, &c. 
In a few cases the white marble has been employed by itself as a 
monolith in the shape of an obelisk, urn, or other device ; but most 
commonly it occurs in slabs which have been tightly fixed in a 
framework of sandstone. These slabs, from less than 1 to fully 2 
inches thick, are generally placed vertically ; in one or two examples 
they have been inserted in large horizontal sandstone slabs or 
“ through-stanes.” The form into which it has been cut, and the 
position in which it has been erected, have had considerable influ- 
ence on the weathering of the stone. 
A specimen of the common white marble employed for monu- 
mental purposes was obtained from one of the marble-works of the 
city, and examined microscopically. It presented the well-known 
granular character of true saccharoid marble, consisting of rounded 
granules of clear transparent calcite, averaging about y^th of an 
inch in diameter (fig. 1, A). Each granule has its own system of 
Fig. 1. — Microscopic structure of white marble employed in Edinburgh tomb- 
stones. A, Structure of the fresh marble. B, Structure of the marble after 
standing eighty-seven years. The black edge is the crust of sulphate of lime 
and town dust which descends along rifts and cleavage planes. 
twin lamellations, and not infrequently gives interference colours. 
The fundamental rhombohedral cleavage is everywhere well de- 
