62 KIMBEBLITE FROM THE UNITED STATES formly distributed throughout the mass. These, however, occasionally disappear, and the whole is serpentine. This olivine and the serpentine together form nearly 75 per cent, of the rock. Besides them other minerals appear in the hand specimen, the most important being pyrope and ilmenite; a few scales of biotite may be observed. Near the exposed surface the rock becomes yellowish, due to the oxidation of the iron, and softer, so that it readily disintegrates.1 The garnet and much of the ilmenite withstand the atmospheric influences, and are found quite fresh and abundant in the sand resulting from the disintegration of the peridotite. The specimens from some localities are quite free from included fragments, while those from another ' are full of fragments of shale, which have been greatly indurated and metamorphosed in the operation.' In the best preserved specimens (which also are free from rock fragments) Mr. Diller estimates the composition to be as follows :—
	He gives a figure of a microscopic section from which it would appear that the larger included minerals are somewhat irregular in outline, size, and distribution. The olivine grains are generally irregular in form, varying from O'l to 1-5 mm. in diameter, and penetrated by many fissures. Occasionally, however, they occur in short prisms, terminated by brachydomes, the usual planes being suppressed. The structure of the matrix appears to be fine-granular. The alteration of the olivine to serpen- 1 Compare the ' yellow ground ' of the mines at Kimberley. - A synonym of anatase (TiO2 ; and corresponding with the perovskite of Williams.