Mt Dryden was the target of this excursion, with three objectives in mind: enjoy the view, look at the rocks, and look at the vegetation.
Mt Dryden is a greenstone outcrop, being volcanic material from the Cambrian era, the oldest rocks in Victoria. It is a particular igneous type with high magnesium, low silica content, with derived minerals including actinolyte which was prized as axe material by aboriginals.
Landholder Graeme Maher met us, and along with Geoff McPhee (previous owner) escorted us to near the summit where the views were quite spectacular. Those with a rock interest collected various specimens, and a good ramble round the peak was enjoyed. We then repaired to the shearing shed for lunch and examined specimens of greenstone axes (and other rocks) found over the years in parts of the Wimmera. Graeme told us about some of the local history including Chinese gardens watered by springs, and how the mountain was now very productive agriculturally with a dense phalaris/ clover pasture supporting prime lambs well-muscled from clambering round the peak.
After lunch, we travelled via the Bolte highway and the Heatherlie-Ledcourt track to a section of the National Park known for having greenstone geology. This was confirmed by finding specimens of greenstone and a volcanic rock (tuff) in that area (Map 351, 501010N, 63036W)
The idea had been advanced that ecology on soils from greenstone rocks (serpentine) is typically different and often contains endemic species to those particular chemical signals (high magnesium/ calcium ratio, possibly toxic chromium and nickel levels.)
The trees were mainly redgum on the low lying parts, changing to yellow box on the rises. The most noticeable feature was the lack of a shrub layer, it generally having an open appearance. Logging had occurred, and probably grazing, and similar landscapes exist elsewhere so the serpentine ecology is only one possibility. However similar soil types in the Black range also seem to be devoid of a shrub layer, so it still looks promising.
The only shrubs present were Banksia marginata (quite large specimens), a long leaved wattle, and Xanthorrhoea. Orchids were thriving in the shelter of the Xanthorrhoeas.
The herb layer was dominated by a prostrate creeping stinking pennywort (Hydrocotyle laxiflora), plus orchids, lilies and stunted grasses.
Orchids noted were:
Slaty helmet, trim greenhood, tall greenhood, wax lip, pink fingers, spiders, gnats, and Diuris pallustris, (swamp diuris or little donkey ). This ? proliferation only occurs where fire has been absent for long periods, and the skirts on the Xanthorrhoea lend support as does the unburnt tops of logged trees . It may be that the absence of a shrub layer helps prevent fierce fires in this ecosystem, leading to the proliferation of orchid species.
Other herb layer plants noted were wall flowers, milkmaids, buttercup, yellow and blue star, brunonia (budding not in flower) and flame heath.
Editor’s note: Many thanks also to Bill for the extensive geology notes he sent everyone enrolled for the day.