So far as the volcanic origin of the diamonds of the Kimberly diamond fields is concerned, Cohen's theory has been generally accepted with the following modifications: that the pipes were not filled by a single volcanic eruption, but by successive eruptions, and that in the case of the Kimberly mine, the pipes contain the results of as many as fifteen successive eruptions. There has, however, been another and more important modification proposed to Cohen's theory, which is far more probable. It will be noticed that Cohen's theory regards the action of the volcanic eruption as only serving to bring fragments of a deep-seated mother rock that contained the diamonds up from below with the material that fills the pipe. Now, Prof. Carvill Lewis proposes the following very important change in Cohen's theory: that the blue ground does not consist of fragmentary material or tuff, but was forced up from below in the pipe in a molten mass and consolidated on cooling. In other words, the blue ground is filled with an ordinary igneous rock that was solidified in place in the vent or pipe.
In the great Kimberly mines the surface of the pipe is divided into numerous separate claims, each consisting of a small square lot. There are so many of these claims in the Kimberly mine that its surface is honey-combed by numerous square pits. The work is done largely by native Kaffirs employed there since the '70's. As the material was removed from the pit, the adjoining claims were separated from each other by high vertical walls.
At a later date, in order to remove the material and separate the lots, high staging provided with ropes and hauling machinery was erected. The number of these ropes is now so great that the mine has the appearance of a huge cobweb.
A very extensive series of investigations has been made at a comparatively recent date by Prof. Henri Moissan of France on various chemical products that are obtained under the influence of the high temperatures of the electric furnace. When a powerful electric current is caused to pass through a highly refractory material, that is to say, a material difficult to fuse, such as carbon, it raises it to an extremely high temperature. A still higher temperature can be obtained by causing a powerful current to flow between two carbon rods that are first brought into contact, and then gradually separated from each other, just as they are in the ordinary arc lights employed for lighting the streets of our cities. In the latter way a temperature that is estimated as high as 3,500° C. (6,332° F.), can be readily obtained. Under these very high temperatures some very curious chemical products have been obtained in electric furnaces. These furnaces consist of small chambers made of highly refractory materials closely surrounding the incandescent carbon, or the carbon voltaic arc. Among some of the most curious of these products are artificially produced diamonds.