The Fossil Forests That Built Australia's Coal: Tasmania's Lurg Hills

On the slopes of Tasmania's Lurg Hills, north of Melbourne, fossil tree trunks lie entombed in sandstone exactly as they fell 280 million years ago. Some trunks stretch twelve metres long, their bark impressions still visible, their branches snapped at the same angle. They are not petrified in the usual sense—replaced by silica or calcite—but preserved as hollow moulds, the original wood having rotted away and left only the void. These are the remains of Glossopteris forests, the trees that would become Australia's black coal.

The Ice Age That Ended in Swamp

The Permian Period began with Australia locked in the heart of Gondwana, straddling the South Pole. Ice sheets kilometres thick scoured the continent, leaving behind striated bedrock and tillite—the lithified mud of ancient glaciers. The Lurg Hills preserve this glacial legacy in their lower rock layers: pebbly mudstones dropped by melting icebergs into cold, dark seas.

Then the climate shifted. By the mid-Permian, around 270 million years ago, the ice retreated. The glacial valleys filled with sediment, and the cold waters warmed. Into this new landscape spread vast forests of Glossopteris, a seed fern with tongue-shaped leaves that dominated the southern supercontinent. These trees grew in low-lying swampy basins along the edge of a shallow inland sea that covered much of what is now Victoria and Tasmania.

The Lurg Hills fossil forest captures this transition exactly. Below the fossil-bearing sandstone lie glacial deposits; above them, coal seams. The sequence reads like a narrative: ice, then forest, then the compressed remains of that forest turned to fuel.

How a Forest Becomes a Void

The preservation at Lurg Hills is unusual. Most fossil wood is permineralised—groundwater carries dissolved minerals into the cell spaces, turning the wood to stone. Here, something else happened.

The trees fell into standing water, probably during seasonal floods. Sand and silt buried them quickly, sealing the wood from oxygen. But the water was acidic, rich in organic acids from the surrounding swamp. Over millions of years, the acids dissolved the wood completely, leaving behind only the bark impression pressed into the sandstone. What remains is a natural cast: the tree's shape, its surface texture, even the growth rings, but no wood at all.

These hollow moulds are called pith casts or mouldic preservation. They are rare because they require precise chemical conditions—enough acidity to dissolve the wood, but not so much that the surrounding sediment collapses. The Lurg Hills contain hundreds of such casts, some still upright, others toppled and aligned as if by a single flood event.

The fallen trunks of the Lurg Hills are not stone trees. They are absences given shape, the ghost of a forest pressed into sandstone.

The Coal That Came After

Above the fossil-bearing sandstone lie the coal seams. These are not the thick, economically important seams of the Latrobe Valley or the Bowen Basin. The Lurg Hills coal is thin and discontinuous, a few metres at most. But it tells the same story.

Each coal seam represents a period when the swamp persisted long enough for peat to accumulate faster than sediment could bury it. The Glossopteris trees that fell and decayed in those swamps became the organic matter that, under pressure and heat, transformed first into peat, then into brown coal, then into black coal. The same trees that left their hollow moulds in the sandstone below contributed their carbon to the seams above.

This is how most of Australia's Permian coal formed—not from tropical jungles, but from cold-temperate swamp forests growing on the margins of a retreating ice sheet. The Lurg Hills preserve both the trees and their transformed remains in a single vertical section, a rare completeness.

A Continent's Fuel Supply

The Permian coal measures of eastern Australia are among the largest in the world. The Bowen Basin in Queensland, the Sydney Basin in New South Wales, and the Gippsland and Bass Basins in Victoria and Tasmania together hold billions of tonnes of black coal. They powered Australia's industrialisation, its steel mills, its power stations.

All of it began with Glossopteris. This single genus of seed fern dominated the Permian landscapes of Gondwana so completely that its fossil leaves are the defining feature of Permian strata across the southern hemisphere. Wherever you find Permian coal in Australia, you find Glossopteris leaves compressed into the rock above and below the seams.

The Lurg Hills fossil forest is not the largest or the most spectacular of these sites. But it is one of the few places where you can stand on glacial tillite, walk through a forest of hollow tree moulds, and then climb up into the coal that forest became. Three chapters of a single story, exposed in a hillside.

The trees fell. The water rose. The swamp deepened. And 280 million years later, the ghosts of that forest still hold their shape in stone, while the carbon of their bodies burns in furnaces across the continent.