The prevailing form of the South African diamonds is that of a rounded crystal, with eight large and a number of minute faces--a form called by crystallographers a _modified octahedron_. Their shapes would be roughly simulated by the Pyramids of Egypt if they could be seen, combined with their reflected images, in a placid lake, or, better to meet the conditions of the country, in a desert mirage. It is a peculiar property of diamond crystals to have convexly rounded faces, so that the edges which separate the faces are not straight, but gently curving. Less frequently in the African mines, but commonly in some other regions, diamonds are bounded by four, twelve, twenty-four, or even forty-eight faces. These must not, of course, be confused with the faces of cut stones, which are the product of the lapidary's art. Geological conditions remarkably like those observed at the Kimberley mines have recently been discovered in Kentucky, with the difference that here the shales contain a much smaller percentage of carbon, which may be the reason that diamonds have not rewarded the diligent search that has been made for them. Though now found in the greatest abundance in South Africa and in Brazil, diamonds were formerly obtained from India, Borneo, and from the Ural Mountains of Russia. The great stones of history have, with hardly an exception, come from India, though in recent years a number of diamond monsters have been found in South Africa. One of these, the "Excelsior," weighed nine hundred and seventy carats, which is in excess even of the supposed weight of the "Great Mogul." [Illustration: Copyright, 1899, by George F. Kunz. FOUR VIEWS OF THE OREGON DIAMOND; enlarged about three diameters. (Owned by Tiffany and Company.)] Occasionally diamonds have come to light in other regions than those specified. The Piedmont plateau, at the southeastern base of the Appalachians, has produced, in the region between southern Virginia and Georgia, some ten or twelve diamonds, which have varied in weight from those of two or three carats to the "Dewey" diamond, which when found weighed over twenty-three carats. It is, however, in the territory about the Great Lakes that the greatest interest now centers, for in this region a very interesting problem of origin is being worked out. No less than seven diamonds, ranging in size from less than four to more than twenty-one carats, not to mention a number of smaller stones, have been recently found in the clays and gravels of this region, where their distribution was such as to indicate with a degree of approximation the location of their distant ancestral home.