Level Two

The photograph looks across the stepped excavation terraces of Hornsby Quarry, the rock walls cutting down through more than 100 m of exposed dolerite to water pooled at the base of the void. The terracing is the record of a working operation: each level marking a period of extraction, the walls growing steeper and the floor dropping further as quarrying progressed through the twentieth century. 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 stepped void visible in this frame. Photographed in 2015, the water at the base of the terraces reflects the full height of the exposed rock walls. The void at that point 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.