100 Transactions of the Royal Society of South Africa. 
9. A flat fragment broken from one end of what, to outside appear- 
ance, must once have looked like a cube of highly crystalline bort. A 
scraping of the broken face with a knife-blade indicates that it consists 
of numerous exceedingly thin successive overgrowths of bort and cement. 
2 carats. 
10. A somewhat hemispherical piece. The central crystal core is 
surrounded by no less than seventeen alternate concentric rings of light 
grey cement and black crystal diamond. 0'4 carat. 
11. A pyramid consisting of a half of a " rounded octahedron." The 
edges, where dodecahedral striations would emerge on ordinary diamonds, 
are here of cement. Rather it looks like a piece of octahedral cement 
with projecting grey crystal bosses on the triangular faces, thus inclining 
the form to that of the plus and minus tetrahedral twin. 0*8 carat. 
12. An irregular lump of cement to outside appearance. When 
first seen it was pitted with small elongated holes as though it had been 
prodded with the point of a penknife. At the time of writing it is scored 
over much of its surface with deep meandering cracks which either are 
(and look like) shrinkage cracks, or were there all the time, but hidden 
by being filled up with cement which afterwards fell out. 2*7 carats. 
13. A fragment similar to 'No. 10, excepting that it has rather 
fewer shells, has an outer coat of shiny bort, and gives the impression 
that the fractured face showing the shells has been glazed over with a 
vitreous layer and polished. The outer contour is that of the cube 
carrying the usual well-defined square indentations. Unlike most hail- 
stone forms, which cleave in the dodecahedral plane, the fractured face 
of this specimen lies in the octahedral plane. 0*5 carat. 
Mr. J. Parry has kindly analysed two small diamonds carrying this 
cement crust. It was not possible to separate the diamond from the cement, 
consequently the specimens had to be treated entire. They gave only the 
familiar indication for iron, and a rather stronger one for magnesia. The 
actual proportions of these elements in the cement itself cannot, of course, 
be determined until a large enough sample can be procured separate. 
Meanwhile it seems reasonable to infer that the comparative softness of the 
cement is due to the magnesia, seeing that a considerable admixture of iron 
with diamond (e. g. stewartite) does not diminish the hardness at all. 
Laminated Diamonds. 
Laminated diamonds are very common. In one sense they appear to be 
examples of the general phenomena of overgrowths, and for that reason are 
included in this paper. 
Suppose a model octahedron of glass to be split parallel to a pair of 
opposite faces into a number of thin laminae ; next the laminae to be sealed 
