Walkway

The walkway runs across the quarry floor like an afterthought, a grey metal structure left standing long after the work stopped. Its connections show rust, its deck dulled by years of exposure inside one of the deepest industrial voids in suburban Sydney. The quarry void at Hornsby reaches approximately 120 metres deep at the southern face and spans roughly 300 metres across, cut through a Jurassic diatreme that geologists now rank as the largest volcanic neck in the Sydney area. Quarrying at Hornsby Quarry began around 1905 when the Higgins family started extracting dolerite from the site. The material, sold as blue metal, was the primary source of crushed aggregate for road construction across northern Sydney for most of the twentieth century. Hornsby Shire Council recognised its strategic value as early as 1912 and purchased the operation outright. Ownership and operational control passed through Hornsby Blue Metal Limited, Farley and Lewers, and eventually CSR Construction Materials before quarrying ceased in 2002. After CSR notified Council on 22 March 2001 that it required the land to be acquired, the NSW Land and Environment Court determined a compensation amount of $26,508,771.28, and ownership passed to Hornsby Shire Council in 2003. The walkway in this photograph records the site in 2015, more than a decade into Council ownership, the quarry floor quiet and the industrial infrastructure standing without purpose. The rock exposed by a century of extraction is itself the geological record: volcanic breccia, columnar jointing, dolerite and surrounding sandstone visible in the quarry's eastern face. The void that the walkway crosses is the same void that geologists would later classify, in a 2022 assessment by Ian Percival, as an internationally significant geoheritage reference site. The walkway was photographed before the NorthConnex spoil delivery of 2017 to 2019 began filling that void with more than one million cubic metres of tunnel spoil. By February 2025, bulk earthworks on the site were complete. The quarry floor the walkway once crossed no longer exists in the form this photograph shows.