The volcanic rocks mainly consist of lava flows and pyroclastic deposits that are exposed at the bridgewater, Nelson and Grant volcanis compoxes. Yhe pyroclastic deposits resulting from phreatomagmatic eruption varu in physical characteristics that are likely caused by fluctuation of magma/water ratio during interaction.
The Newer volcanics are basaltic materials which over the past 4.5 Ma (since early Pliocene) have spread from central Victoria through western Victoria to southeastern South Australia. They also include some limited lava flows in eastern Victoria.