314 Professor T. G. Bonney — Parent-rock of the Diamond. 



2. A fragment (probably about one-quarter) of a flattisb ovoid 

 boulder. — The two broken surfaces, which are nearly at right angles, 

 measure 5 and 5^ in. roughly, and it is about 31 in. high. The rock 

 very closely resembles the one just described, except that mica 

 occurs rather oftener and in larger flakes ; perhaps the garnets (here 

 also not quite I'egularly distributed) are slightly more numerous. 

 The outer surface is not quite so well preserved, though enougb 

 remains to show that it also has been smooth, and a few thin veins 

 of a white mineral (calcite ?) 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 (octahedron), apparently about 0-liu. 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-coloured 

 kelyphite rim of the latter, which is about 0-03 in. 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 commonly 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 tlie constituents 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 altered 

 carbonate. There is no real difference between this eclogite and the 

 last-named one. 



Eclogite Boulders without Diamonds. 



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

 diameter. — In macroscopic aspect 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 

 conspicuous 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 3^ in. It retains a good piece of the 

 outer surface, which, though now a little corroded, was once smooth. 

 The rock, which is rather decomposed and crumbly, consists chiefly 

 of three minerals : garnet, not quite so large, paler and more pink 

 in colour than the last-named ; an emerald-green pyroxene, and 

 a yellowish or greenish grey, platy to fibrous mineral, suggestive 



several opportunities of studying eclogite, and have no doubt as to its origin. Take 

 away the alkali from a magma with the chemical composition of a diorite, and th& 

 result would be garnets in place of felspar, i.e., an eclogite. 



