These stones are considered by some writers as varieties of quartz (76), and by others as a kind of opal (102). They are sometimes found in Hanover, but are chiefly brought from the island of Ceylon. It is usual to cut them before they are exported, and generally in a convex and oblong form, without facets, and in such manner as to bring the streak which intersects them into the centre. Among the king of Candy’s jewels, which were sold by auction in London, in June 1820, was a cat’s─eye of extraordinary magnitude and beauty. It was two inches in diameter, of dark colour, and nearly hemispherical. This stone was set in gold, with small rubies round it, and was sold for more than 400_l._ Cat’s─eyes are chiefly used for setting in rings. Their size seldom exceeds that of a hazel nut; but there was one in the cabinet of the Dukes of Tuscany, which was nearly an inch in diameter. Those that are the most highly esteemed are of an olive─green, or red colour. 87. _WOODSTONE is a very hard mineral substance, supposed to have been wood petrified with a siliceous mineral called hornstone._ _It is of various colours; and has not only the external appearance, but the internal organization of wood._ This extraordinary mineral is found embedded in sandy loam, in alluvial soil (269), and occurs in various parts both of Europe and Asia. It has been found in ferruginous sand, near Woburn, in Bedfordshire, and near Nutfield, in Surrey. Immense pieces of it are discovered in some places in the original shape of the trees; trunks, branches, and roots. In the year 1752 the whole under part of the trunk of a tree, with its branches and roots, was found, in a state of woodstone, near Chemnitz, in Saxony; and, in the Electoral Cabinet at Dresden, there is part of the trunk of a tree, from the same place, which measures five feet in length and as many in thickness. Woodstone is in considerable request by lapidaries. It takes a good polish, and is made into beads for necklaces, and other female ornaments. In the East Indies it is generally called _Petrified Tamarind Tree_. 88. _COMMON SAND is a granulated kind of quartz; or consists of rounded grains of small size, which have a vitreous or glassy surface._ _It is usually of white or yellowish colour; but is sometimes blue, violet, or black._ In the torrid regions of Africa and Asia there are immense tracts of desert covered only with sand, so dry and light as to be moveable before the wind, and to be formed into vast hills and boundless plains. These are incessantly changing their place, and frequently overwhelm and destroy the travellers whose necessities require them to enter these dreary realms.