520 
Proceedings of the Royal Society 
• 
saccharoid Italian marble. I have also observed a pink Italian 
shell-marble, and a finely fossiliferous 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 ha» 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 maTble-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 
A B 
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- 
