l68 THE ORIGIN AND FORMATION OF THE DIAMOND. 



Replying to some objections that have been made against 

 the formation of the diamond in the mines themselves, Hatch 

 and Corstophine, in their Geology of South Africa say : — 



" But the facts so far known do not in any way controvert the view that 

 the blue ground, or the rock from which it was derived, is itself the 

 original matrix of the diamond. The fragmental character of many of 

 the diamonds is as explicable on the assumption that they were formed 

 in the molten magma and broken in the movements that went on in the 

 pipes as it is on the assumption that the diamonds were derived from some 

 foreign rock." 



Assuming, then, that the diamonds were formed in the mines 

 themselves, and leaving the molten-iron theory for future con- 

 sideration, there still remains the very important question to 

 decide as to the stage in the evolution of the diamond mines at 

 which the diamonds were formed. Were they formed in the 

 olivine rock, when it was first in a molten condition, or were 

 they formed later on, when it had become mixed with water 

 and steam, and had attained the mud -volcano stage that pre- 

 ceeded its eventual solidification ? I have always felt that the 

 answer to this question, and indirectly the solution of the problem 

 before us, turned largely on the question of the temperature at 

 which the diamond was formed, and if we can succeed in fixing 

 a maximum limit to the temperature at which diamonds 

 were formed in the pipes, we shall have taken a great step to- 

 wards the solution of the problem. After a careful and prolonged 

 consideration of the evidence available, I have come to the 

 conclusion that the diamonds were formed in the mines after 

 the latter had reached the mud-volcano stage ; and the object 

 of this paper is mainly to attempt to establish that view. 



Let us first consider what are the facts against the diamonds 

 having been formed in the molten volcanic rock. 



In the De Beers Mine there is a dyke of volcanic rock that 

 goes locally by the name of the " snake." This dyke of volcanic 

 rock, together with similar dykes that have been found out- 

 side the actual margin of the mine, has been found by most 

 careful microscopical and other examination to be exactly similar 

 to the blue ground as it occurs in the mines, excepting that the 

 latter has undergone more disintegration from the prolonged 

 action of steam and hot water to which it was later exposed. 

 In other respects, however, these are practically identical and 

 there seems to be no doubt that the volcanic dykes and the blue 

 ground, as we now know it. had the same common origin from 

 below. Yet the most careful examination has failed to show 

 the presence of diamonds in the unaltered volcanic rock. I 

 repeat, that, so far as we know, no diamonds have ever been found 

 in South Africa in any rock that has remained unaltered just as it 

 was poured out from the volcano. In all cases where diamonds are 

 found, the rock has undergone considerable subsequent alteration. 

 That is a very significant fact. Besides the fact that diamonds 

 are never found in unaltered volcanic rock, experiment supplies 

 us with other facts that seem to prove conclusively that they 

 could not have existed for any length of time in contact with 

 the molten rock without being destroyed. Experiments carried 



