lavas of this kind at all common. A small outcrop at Spring Hill in Victoria, Australia has tachylite which has been exploited as a material for making Aboriginal flaked stone implements. Dike and sill sources A third mode of occurrence of tachylite is as the margins and thin offshoots of dikes or sills of basalt and diabase. They are sometimes only a fraction of an inch in thickness, resembling a thin layer of pitch or tar on the edge of a crystalline diabase dike, but veins several inches thick are sometimes found. In these situations tachylite is rarely vesicular, but it often shows very pronounced fluxion banding accentuated by the presence of rows of spherulites that are visible as dark brown rounded spots. The spherulites have a distinct radiate structure and sometimes exhibit zones of varying color. The non-spherulitic glassy portion is sometimes perlitic, and these rocks are always brittle. Common crystals are olivine, augite and feldspar, with swarms of minute dusty black grains of magnetite. At the extreme edges the glass is often perfectly free from crystalline products, but it merges rapidly into the ordinary crystalline diabase, which in a very short distance may contain no vitreous base whatever. The spherulites may form the greater part of the mass, they may be a quarter of an inch in diameter and are occasionally much larger than this. These coarsely spherulitic rocks pass over into the variolites by increasing coarseness in the fibers of their spherulites, which soon become recognizable as needles of feldspar or feathery growths of augite. The ultimate product of decomposition in this case also is a red palagonitic substance, but owing to the absence of steam cavities the tachylite selvages of dikes are more often found in a fresh state than the basic lapilli in ash-beds. Many occurrences of basaltic pitchstones have been reported from Skye, Mull, and the western part of Scotland; they are found also in connection with the intrusive diabase sills in the north of England and the center of Scotland. In the Saar district of Germany similar rocks occur, some of which have been described as weisselbergites (from Weisselberg). Other localities for tachylites of this group are New Providence, Silesia and Sweden. See also Notes References Mafic rocks Vitreous rocks