The Parent-rock of the Diamond in South Africa. 229 



•surface is not quite so well preserved, though enough remains to show 

 that it also has been smooth, and a few thin veins of a white mineral 

 (calcite 1) traverse the rock. On this surface, near the meeting of the 

 two fractures, and exposed by the removal of a little material 

 (i.e. it might originally have been just hidden) is a diamond (octa- 

 hedron), apparently about 0*1 inch in diameter. On one side it rests 

 against a pyrope, the adjacent surface of which is incurved, the 

 two minerals being parted by the dull green-colourecl kelyphite rim 



Fig. 2. — Garnet and diamond (diagrammatic, nearly twice natural size). 

 (1) Diamond, (2) garnet, (3) kelyphite rim. 



•of the latter, which is about 0*03 inch in thickness. Thin sections of 

 this boulder correspond almost exactly with those from the other, the 

 garnets showing precisely the same tints, though traces of a cleavage, 

 (roughly parallel throughout) are perceptible on close inspection, and 

 are distinct under the microscope. In garnet such a structure com- 

 monly indicates pressure, and the general parallelism accords with this 

 explanation, but the other constituents show no signs of crushing. 

 The " kelyphite " rims to the garnets are perhaps slightly broader and 

 the brown mica passes into a green (chloritic *?) mineral, and occupies 

 cracks in the garnet a little more frequently, but as before the con- 

 stituents tend to lie parallel rather than radially. One or two of the 

 diopsides show fine oscillatory twinning. The cracks are occupied with 

 calcite or some allied carbonate. There is no real difference between 

 this eclogite and the last-named one. 



Eclocjite Boulders without Diamonds. 



3. Part of a boulder, which must have been about a foot in 

 diameter (found at 250 ft. level). It presents a general resemblance to 

 the rocks described above, with, however, the possibility of a second 

 green constituent. This is not confirmed on microscopic examination. 

 The rock consists, practically, of pyrope and diopside, as already 

 described, except that negative crystals are rather unusually con- 

 spicuous in the latter. Into the details of these, as the point seems 

 not to have any bearing on the present investigation, I do not purpose 

 to enter. 



4. A fragment, more irregular in form than the others, measures 

 very roughly, about 7 in. by 4f 'in. by 3J in. It retains a good piece 

 of the outer surface, whi^h, though now a little corroded, was once 



