the history of fossils, a genus of crystals, the figures of which are influenced by an admixture of some particles of tin.

The cassiteria are of two kinds; the whitish pellucid cassiterion, and the brown cassiterion. The first is a tolerably bright and pellucid crystal, and seldom subject to the common blemishes of crystal: it is of a perfect and regular form, in the figure of a quadrilateral pyramid: and is found in Devonshire and Cornwall principally. The brown cassiterion is like the former in figure: it is of a very smooth and glossy surface, and is also found in great plenty in Devonshire and Cornwall.