In Tasmania sedimentary rocks containing shelly fossils at many horizons, some graptolitic horizons and numerous conodont horizons were deposited, apparently continuously, from the Tremadoc Epoch into and after the Llandovery Epoch. Superposition can be demonstrated over this interval so that the position of preserved faunas or biotas relative to one another is clear in most cases. Twenty successive Ordovician faunas are recognized. During the interval represented by this succession the geographical affinities of the faunas were generally with eastern Asian, North American and South American faunas, but in the later part of the Ordovician and in the Silurian the affinities were wider. Because of the clarity of the succession, the duration of deposition and relationships of the faunas, the Tasmanian succession is likely to be a useful link in world correlation, especially for isolated areas such as parts of South America and southeastern Asia.