Professor T. G. Bonneij — Parent-voclc of the Diamond. 319 



and felspar, variable in size, embeddecl in a dusty matrix, including 

 a carbonate, wliicli is more abundant within about a fiftieth of an 

 inch from the junction. This part is slightly stained, but I was 

 unable to detect any signs of contact metamorphisin. Specimens (ii) 

 and (iv) are generally similai", but the former contains some small 

 I'ounded bits of varieties of diabase, and one may represent 

 a crystalline limestone. The veins are filled with calcite and other 

 secondary products, and are bordered by a very thin film of a brown 

 micaceous mineral, like that described as often permeating the 

 * blue.' Both specimens suggest micromineralogical changes, such 

 as might be produced by the passage of hot water. 



Other specimens of the sedimentary rock in the immediate neigh- 

 bourhood of the blue have been forwarded to me by Mr. Trubenbach ; 

 one, from the adit on the southern side of the section mentioned 

 above, is a grey mudstone, containing a flattish rectangular pebble, 

 of a dark-green compact rock. Two others are from No. 2 mine, or 

 about 700 yards to the south-west. One, struck in the shaft at 

 a depth of 200 feet, is a conglomerate, composed of well-rounded 

 rock fragments, with some scattered grains of quartz. Eacli of the 

 former is bordered by a zone of a crystalline carbonate (irapui'e 

 calcite), and the interstices are filled, sometimes by a clearer variety 

 of the same, but more often by some minutely granular secondary 

 product. Of the rock fragments, one is a subcrystalline dolomitic 

 limestone ; two, perhaps, are chalcedony ; the remainder are igneous ; 

 the majority being varieties of diabase, sometimes rather decomposed ; 

 the rest trachytes, mainly andesites. Their general aspect and the 

 not unfrequent presence of vesicles (now filled with viridite) suggest 

 that they have been furnished by lava-flows. Another specimen, 

 obtained in the same working at a depth of 400 feet, is a rather 

 felspathic diabase, not unlike one of the varieties in the conglomerate. 

 It is a good deal decomposed, is not improbably from a lava-flow, but 

 does not call for a minute description. 



Conclusion. 



Thus the diamond has been traced up to an igneous rock. The 

 '■ blue ground ' is not the birthplace either of it or of the garnets, 

 pyroxenes, olivine, and other minerals, more or less fragmental, 

 which it incorporates. The diamond is a constituent of the eclogite, 

 just as much as a zircon may be a constituent of a granite or a 

 syenite. Its regular form suggests not only that it was the first 

 mineral to crystallise in the magma, but also a further possibility. 

 Though the occurrence of diamonds in rocks with a high percentage 

 of silica (itacolumite, granite, etc.) has been asserted, the statement 

 needs corroboration. This form of crystallised carbon hitherto has 

 been found only in meteoric iron (Canyon Diablo), and has been 

 produced artificially by Moissan and others with the same metal as 

 matrix. But in eclogite the silica percentage is at least as high as 

 in dolerite ; hence it is difficult to understand how so small an 

 amount of carbon escaped oxidation. I had always expected that 

 a peridotite (as supposed by Professor Lewis), if not a material yet 



