ABSTRACT
This chapter summarizes the distribution stratigraphy and structure of the rocks which comprise the Wianamatta Group. The Hawkesbury Sandstone is overlain by a series of fine grained rocks the Wianamatta Group, the uppermost unit of the thick Permo-Triassic sequence which infills the Sydney Basin. The Mittagong Formation is composed of alternating black siltstone and sandstone bands and lenses of varying thickness. The Wianamatta Group with a maximum recorded thickness of 304 m is divided into the 'Ashfield Shale', the 'Minchinbury Sandstone' and the 'Bringelly Shale'. As described the Wianamatta Group re- presents a sequence of fine grained rocks which underlie a major portion of western Sydney and the Cumberland Plain. The rocks when fresh commonly range from medium to high strength, with closely spaced defects in the form of jointing and bedding plane partings and on exposure tend to slake.
