ABSTRACT
The Older Volcanics are essentially part of the Werribee Formation, partly buried beneath the sequence of later Tertiary and Quaternary sediments and basalts. The Older Volcanics occur at or close to the surface in the western half of the Central Business District and a band of outcrops occurs generally northwest to Tullamarine and to the south and southeast through South Melbourne. The Older Volcanics basalts in the Melbourne area are of alkali olivine type. The Older Volcanics of the Melbourne area consist of flows of basaltic lavas and deposits of pyroclastics and volcanoclastic sediments. The pyroclastic components include scoria, lapilli tuff and ash. Age determinations of the Older Volcanics in the Melbourne area have been obtained by potassium/argon dating of the rock and by analysis of fossil pollen in interbedded sediments. The basalt lavas of the Older Volcanics mostly have fine grained to glassy texture and are generally dense with close joint spacing.
