254	THE DIAMOND
	that some extraordinary rich yields reported in the early days, covered additions by purchase of stones from undisclosed sources. It is generally acknowl­edged that the volume of illicit trading was very large, and it is equally certain that the most successful traders escaped detection. As such transactions could be con­cealed in no other way so readily, nor the purchases be disposed of so easily, the presumption is that among so many, some of the claim owners took advantage of the situation. There has been an apparent decrease in the yield per load of most of the mines as they have been carried deeper. The De Beers and Kimberley have steadily declined from over one carat per load in 1888 to .80 of a carat in 1898 and 0.37 in 1908. The Du-toitspan, which from the beginning gave a small average yield, has nevertheless held very steady, dropping by one hundredth of a carat only in the yearly average from .26 in 1905 to .23 in 1908. When first reopened in 1904 the yield was only .12. The yield of the Wesselton also has been very uniform, being the same in 1908 as it was in 1898, i. e., .27 of a carat per load. In the interim it has never been less than .28, and in 1907 it was .32. The Bultfontein shows an increase from 1902, when the yield was .21 of a carat, to .41 in 1905, since which it dropped again to .32 for 1908. The increase of the first four years after the consolidation began to operate it, is accounted for by the fact that there was an ac­cumulation of poor material which was first cleaned up. The Koffyfontein runs even: .473 in 1906 and .476 in 1907. Of the open-cut mines, the Premier of the Transvaal shows the greatest decline in average yield. In the be-