Level Two

Diamond-patterned mesh screens a doorway opening in a stripped interior at the Hornsby Quarry processing plant. Light spills across the floor, revealing scattered straw debris, a pair of ribbed ventilation hoses propped against the concrete block wall, and a stone grinding wheel resting where it was left. Straw is compressed against the ceiling joists, with loose falls gathered at the base of the screen. The quarry sits within the Hornsby diatreme, a large oval volcanic structure approximately 1.5 km across at its longest axis. The diatreme is the largest volcanic neck in the Sydney Basin, formed in the Jurassic period between 146 and 200 million years ago, extruding through the sandstone deposits of the Sydney Basin. Quarrying exposed a cross-section through that volcanic neck that geologists now rank as internationally significant. Dolerite extraction began on the site around 1905 under the Higgins family, whose ancestors had farmed Old Mans Valley since the 1830s on volcanic soil far more fertile than the surrounding sandstone country. Hornsby Shire Council purchased the quarry in 1912, recognising the strategic value of local dolerite for road construction. Operations passed through several operators over the following decades, including Hornsby Blue Metal Limited, Farley and Lewers, and ultimately CSR Construction Materials, before quarrying ceased in 2002. The crushed dolerite produced here was the primary blue metal source for road base across northern Sydney throughout most of the twentieth century. At its recorded extraction rate of approximately 110,000 tonnes per year, the quarry cut steadily deeper, leaving the void beyond these walls. Photographed in 2015, the plant had been idle for more than a decade. Within two years, more than one million cubic metres of spoil from the NorthConnex tunnel project would begin filling it.