The Rouchel district in eastern New South Wales is about 100 km northwest of Newcastle and occupies an area of about 1200 km- between the towns of Parkville, Scone, Aberdeen, and Muswellbrook in the west, and the Mount Royal Range in the east (Fig. 1). Carboniferous sedimentary and volcanic rocks in the Rouchel district are part of the New England Belt of the Palaeozoic Tasman Geosyncline (Fig. 2). During the early Palaeozoic the Tasman Geosyncline, an orthogeosyncline as defined by Kay (1951) contained the Lachlan and New England Belts; the Lachlan Belt ceased to be part of the geosyncline after the Middle Devonian Tabberabberan Orogeny, but geosynclinal conditions persisted in the New England Belt until late Palaeozoic time. Throughout the Late Devonian and Early Carboniferous the Rouchel district occupied a subsiding shelf, the Tamworth Trough, adjacent to and east of the Tabberabberan orogen. Conditions of sedimentation on the shelf were, in general, initially marine but later became progressively non-marine from west to east; a sequence 4000 to 4500 m thick was deposited between Late Devonian or Early Carboniferous and the medial Early Carboniferous (middle Visean).