a

and allied to eclogites. At a meeting of the Royal Society he presented his conclusions:

The blue ground is not the birthplace either of the diamond 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. ** I had always expected a peridotite (as supposed by Professor Lewis), if not a material yet more basic, would prove to be the birthplace of the diamond.

Can it possibly be a derivative mineral, even in the eclogite? Had it crystallized out of a more basic magma, which, however, was still molten when one acid more was injected and the mixture became such as to form eclogite? But I content myself with indicating a difficulty and suggesting a possibility; the fact itself is indisputable that the diamond occurs, though rather sporadically, as a constituent of an eclogite, which rock, according to the ordinary rules of inference, would be regarded as its birthplace.

Professor Bonney's statement that diamonds occur in the eclogite of the Newlands mine caused me to examine the eclogite which is found in all the mines at Kimberley and has always been treated as waste rock and thrown away. There are tons of it lying about the Kimberley mines. I have examined hundreds of pieces of this rock, but never found a diamond, nor have I ever heard of a diamond being found in it by anyone during the many years that these fields have been worked. I caused about 20 tons to be collected and sent to a test plant, where it was crushed and afterwards jigged, but it contained no diamonds. Surely if one could find diamonds in the eclogites of a poor mine like the Newlands, the total diamond yield. of which was only a few hundred carats, one would naturally expect to find them in the eclogites from mines in the vicinity of Kimberley, which are so rich.

Mr. Waldemar Lindgren, who is connected with the United States Geological Survey, has had an opportunity of studying the blue ground and the minerals contained therein from samples supplied by the writer from which 45 slides were made. His conclusions are as follows:

In looking over the literature [on diamonds], especially the papers by Profs. A. W. Stelzner and T. G. Bonney, it seems to me that the connection of the diamond with the garnet in the peridotite and pyroxenite has been satisfactorily proved. It is not possible to regard it as formed in the "blue ground." On the contrary, it was evidently contained in the peridotite magma and crystallized with it.

A specimen of the rock, which I presume to be similar to the eclogite spoken of by Professor Bonney, taken from Dutoitspan mine, was handed to Dr. G. F. Becker, who had a slide made from it. He determined the rock to be lherzolite, and says:

a Proceedings of the Royal Society, Vol. LXV, July 27, 1899.

This composition shows that the rock is extremely analogous to kimberlite; in fact, probably a subvariety of it. Zirkel considers kimberlite as closely allied to lherzolite, while Rosenbush appears uncertain how to classify it.

Doctor Becker is still of the opinion that diamonds ought to be found in the lherzolite in spite of the result of the test of 20 tons. Quite a number of specimens of diamonds and garnets cemented together have been found, but in most specimens which have come under my observation the diamond has grown into the garnet. A diamond was found (January 9, 1904) in Wesselton mine, Kimberley, which had a small garnet embedded in it. The diamond weighed 114 carats, and the garnet was estimated to weigh about half a carat. It appeared to fill the hole in which it was embedded. The diamond was of cubic crystallization with nearly half of the cube wanting. The part of the diamond in which the garnet was buried had numerous depressions similar to the one containing the garnet, and one is led to think that these depressions were also once filled with small garnets, or, in other words, the diamond crystallized upon a nest of garnets. It was of a peculiar plumbago color and semitransparent. All of the diamonds crystallized in cubic form which have been found of late in Wesselton mine were of this peculiar color. Specimens have also been found where the diamond was embedded in olivine.

5. Sir William Crookes and others have mentioned diamonds which burst or explode on being brought to the surface; and Sir William says it has been "conclusively proved that the diamond's genesis must have taken place at great depths under enormous pressure. The explosion of large diamonds on coming to the surface shows extreme tension."

Professor Lewis says that Kimberley diamonds have been found sometimes to have optical anomalies due to strain. Fizzan thought this strain to have been caused by the unequal distribution of heat during cooling; but Jannettaz holds that the strain is due to compressed gas in the interior of the crystal.

I have found that the light-brown smoky diamonds frequently crack when brought from the mine to the surface; but even these remain intact if kept in a moist place. In the days of open-cut working, when a smoky or light-brown diamond was found, the digger placed it in his mouth, where he kept it until he offered it for sale. The buyer placed it in a raw potato, in which it was shipped to Europe. The temperature of the ground in which the stone was found would, as a rule, not exceed 70° F. The temperature of the diamond would be raised to 98° F. while in the digger's mouth. If, however, the stone was kept in a dry place, even at a lower tempera

a Bulletin de la Société Minerale de France, II, 1879, p. 124.

ture, it would crack in all directions. One might argue from this that it was not the expansion of gases by heat alone which caused the fractures. If these fractures were due to compressed gas, as contended by Jannettaz, one might expect this cracking to have occurred while the diamond and its contained gas were exposed to the enor mous heat to which, according to the igneous theory, diamonds must have been subjected.

I had been led to believe that only light-brown or smoky stones crack on being exposed to dry air, but I have lately been informed by one of the old diamond miners that he had seen white stones which showed the same phenomenon. There are innumerable fragments of diamonds in the Kimberley pipes, and it is a question how the original crystals became fractured.

6. Sir William Crookes says that the ash left after burning a diamond invariably contains iron as its chief constituent, and the most. common colors of diamonds, when most perfectly pellucid, show various shades of brown and yellow from the palest "offcolor" to almost black. These variations, he declares, accord with the theory that the diamond has separated from molten iron.

I have made exhaustive tests in order to ascertain whether diamonds contain iron, oxidized or metallic. The experiments were made with a magnetic separating machine, the field magnets of which attracted any mineral containing iron or iron oxides except pyrites. Although some of these diamonds had the appearance of being coated with iron, and others were colored dark brown and deep yellow, they were in no way attracted by the magnet, even when excited by a strong electric current. These experiments do not, perhaps, disprove the existence of iron in the diamond, but they do establish the fact that the quantity is infinitesimally small. Further experiments in this direction ought to be made by those who have better facilities for such work than are at our disposal here in Kimberley. The experiments of Messrs. Hannay, Moissan, Friedel, Sir William Crookes, and others all show that microscopic diamonds can be produced artificially; but they throw very little light upon the question how the diamonds in the South African craters crystallized.

7. From what is known of the theory of crystallization, one is inclined to the old Indian idea that diamonds grow like onions, though much less quickly. It is hardly conceivable that diamonds, such as the Koh-i-nur, the Great Mogul, the Excelsior (a Jagersfontein South African stone of 971 carats), the two largest De Beers diamonds (respectively of 503 and 428.5 carats), and the Cullinan from the Premier mine (3,025 carats), were formed, as the microscopic diamonds have been, in a moment of time during the sudden cooling of molten iron.

Is it not more reasonable to suppose that these enormous crystals grew little by little, and that nature has followed the same laws of crystallization in the diamond as in other minerals?

In March, 1904, a diamond of 228 carats was found in the Kimberley mine, which contained two red spots in the center of the stone. One of these was bright red, and, under a magnifying glass, was found to be a small diamond with crystalline faces easily distinguishable. The large diamond was cracked in all directions around the small crystal for a distance of about one-sixteenth of an inch.

I have been frequently asked " What is your theory of the original crystallization of the diamond?" and the answer has always been "I have none, for after nineteen years of thoughtful study, coupled with practical research, I find that it is easier to drive a coach and four through most theories that have been propounded than to suggest one which would be based on any nonassailable data." All that can be said is that in some unknown manner carbon, which existed deep down in the internal regions of the earth, was changed from its black and uninviting appearance to the most beautiful gem which ever saw the light of day.