In 1874 an account of the chemical and optical properties of the yellow and blue ground, and the contained minerals was given in London to the members of one of the learned associations there by Prof. N. Story-Maskelyne, F. R. S., keeper, and the late Dr. W. Flight, assistant, of the mineral department, British Museum, and although rather technical in character will no doubt be interesting to those who would like to make themselves acquainted with the formation of the diamond mines. Extracts from this account will show the nature of the rock commonly but erroneously called the matrix of the diamond, and also furnish a list of minerals found in the samples furnished to the above mentioned scientists. Alluding to the yellow and blue these gentlemen say: “Ground mass, pulverulent, soapy, light yellowish in the upper, and of an olive-green to bluish gray color in the lower regions of the excavations, is a hydrated bronzite. Through it is disseminated a considerable amount of vermiculite.... In this ground mass fragments of shale and a micaceous looking mineral—sometimes an important constituent.... It is a mineral of the vermiculite group.... Ferriferous eustatite (bronzite), prismatic crystals of a bright green color not infrequent, of the size of canary seeds—colored brilliant green by nickel.... Hornblendic mineral accidental—closely resembling smaragdite garnet. Ilmenite.[26]... Diallage much altered, opaline silica, sometimes resembling hornstone. Calcite. Bronzite, small bright green crystals, with something of an emerald tint, prismatic; angle 87° 20′. Hydrated bronzite; drab (or pale buff tint) much broken up, and cemented by calcite in bar-like forms, resembling feldspar.... Through it is disseminated a considerable amount of vermiculite—vaalite—surface of a fine bluish green like that of clinochlore, giving color to the mass. Hexagonal prisms 60° and 120°, resembling halite. Garnet zircon, brownish white. Hornblende crystals, with the appearance of smaragdite. Grossular garnet. Brilliant little black tourmalines. Smaragdite:—brilliant grayish green fragments of crystal, angle 125° 15′ equal to hornblende type. Olivine, steatite; variety of vermiculite, or a ferriferous eustatite or bronzite. Transparent striated mineral, of fibrous irregular outline, augitic cleavage; pale brown, in some lights a violet tinge. Between the fibres minute bars of brown vaalite, but tolerably free from calcite; occasionally associated with a yellow wax-like substance, probably opal. This striated mineral may be regarded as made up of Bronzite 43.850 Hydrated bronzite 24.017 Opaline silica 30.895 Alumina .970 Chromium oxide .251 —————— 99.983