TASMANIA, a State of the Commonwealth of Australia consisting of one large and numerous smaller islands, the largest of which, King, Flinders and Cape Barren Islands, lie in Bass Strait (total area, 26,215 miles—roughly that of Scotland—form ing 0.88% of the area of the Commonwealth). The island of Tas mania extends from about lat. 4o' S. to lat. 4o' S., is of a maximum length (N.–S.) of 180 m. and breadth (E.–W.) of 190 miles, and has a shield-shaped general outline tapering southwards. It lies upon the main continental platform and at various periods formed part of the continent to its north. Bass Strait, though some 140-15o miles wide, is relatively shallow so that Tasmania is linked to the mainland by a submarine ridge carrying only 3o-4o fathoms from which rise the groups of islands mentioned above. The latest severance of Tasmania is probably geologically recent and a rise of C. 200 ft.—or a corresponding fall in sea-level would reunite it to the mainland. It is, in fact, essentially a por tion of the eastern highland belt of Australia (see AUSTRALIA: Geomorphology) and has the same general physiographic charac ter modified, to some extent, by climate. Subjected to repeated strains and stresses, and also to active denudation, throughout its history, the island-mass has assumed the character of an ex tremely irregular upland block, or group of blocks, with generally flattened tops but steep, and often precipitous (step-faulted) sides—cf. the term "tiers"—and possessing several coastal, and also some inland, lowlands in which crustal oscillations have produced features of both emergence and of submergence. The nearness in time of some of the most influential of these move ments is proved by the freshness and sharpness of many of the forms (e.g., "drowned" coastal features, valley gorges, water falls and generally ungraded stream courses), by the signs of dislocated drainage, and by the general irregularity, and even wildness, of the topography. The extensive and varied igneous intrusions—Palaeozoic granites and serpentine, Cretaceous dia base, Tertiary basalts, etc.—evidence the intensity of the move ments, while weathering has flattened, but also in part, by means of differential erosion, diversified the surface.
The general surface level rises to some 4,000 ft. with many sum mits approaching 5,000 ft. (Cradle Mountain, 5,069 ft.), but the incision of streams and the cutting of deep valleys and gorges (King River, 3,00o ft. deep, and cf. the valleys of the Arthur, Pieman, Gordon Rivers) has given rise to a wild, inaccessible, and little known landscape, with some lakes and forests, much poor and sterile rock and soil, but possessing great actual and potential mineral wealth. (ii.) The Central (Lake) Plateau, only partly dissevered from the above, consists mainly of Mesozoic rocks (Permo-Carboniferous) and slopes down from a general level of 3,500 ft. in the northwest to lower levels in the southeast, in which direction it is drained by the streams of the Derwent system. To the north and northeast it presents a towering es carped front ("tiers") with individual elevations of over 4,00o ft. fashioned mainly out of igneous (diabase) intrusions. The rocks contain some oil shale and coal, but for the rest supply only grasslands. The heights which flank the central east coast are a portion of this formation, being,severed only by the Macquarie Coal River depression (elevation 66o ft. near Tunbridge). (iii.) The northeast highlands, though detached from the central massif by the broad Tamar-Esk depression, resembles it in being a pla teau with levels rising to 3,000-4,000 ft. The Palaeozoic sediments have been penetrated by igneous intrusions of various dates and composition (granite, diabase, basalt), the harder of which form great bosses (Ben Lomond, highest elevation in the island, 5,16o ft.). They constitute a group of wild and mineralised mountain blocks towering above the adjoining lowlands. (iv.) The northern lowlands a down-faulted area fronting Bass Strait and broadest in the northwest, consist substantially of the same rocks as the highlands behind (pre-Cambrian schists, Palaeozoic slates, sand stones, etc.) and, besides rich deposits of metallic ores, include valuable limestones, oil-shales and coal. Many of these rocks yield infertile soils, but the great basalt (Tertiary) flows which characterise this area redeem this quality, and these lowlands, with their irregular terrain and diversified potentialities form one of the richest regions. (v.) The east and southeast lowlands are even more irregular, and are worked out mainly in Mesozoic (Triassic–Jurassic) strata which contain coal. Diabase and older rocks form irregular, rough and infertile ranges, spurs and plat forms over considerable areas, but the later strata yield soils useful for pasturage and cultivation.