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HISTORY
The first mention made of Prospect Hill was in 1789 when Captain Tench observed the barrier of the Blue Mountains to the west from its summit. The area was attractive to farming due to the richness of the soil and a two-square-kilometer grant was taken up by Lt. William Lawson in the late 18th century.
The outcropping chilled margin of basalt was noted by Charles Darwin in 1836 and it was mentioned in his writings on the voyage of the Beagle. The columnar nature of the basalt exposed in a small quarry was pointed out to J. D. Dana by geologist Rev. W. B. Clarke when the American Fleet moored in Sydney Cove in 1839 (Dana, 1849).
Road surfacing material has been obtained from Prospect Hill since the early 1830's, long before Government Geologist C. S. Wilkinson reported on the economic potential of the deposit in 1879. Prospect quarry itself was opened as the Emu quarry in 1883 by Sperring and Partner, who were bought out by Emu and Prospect Gravel and Road Metal company in 1900. The latter company was in turn taken over in 1919 by New South Wales Blue Metal and the name changed to New South Wales Associated Blue Metal Quarries. Blue Metal Industries was formed in 1954 and this company was recently bought out by Boral Resources (N.S.W.) Pty. Ltd., who continue to operate the Prospect quarry on a large scale (Clark, 1976).
GEOLOGY
The intrusion forms a prominent landmark which rises to 60 m above the surrounding country and 122 m above sea level. It is 2.4 km long and 1.4 km wide. The periphery of the intrusion has been exposed by erosion and this, together with its proximity to the rapidly expanding city of Sydney, 29 km to the east, led to its early exploitation as a source of construction material.
The Prospect Intrusion is a Jurassic doleritic laccolith emplaced concordantly between Triassic deltaic Hawkesbury Sandstone and the overlying lacustrine Ashfield Shale member of the Wiannamatta Group, also of Triassic age. Thin remnants of the Ashfield Shale underlie the intrusion in some areas.
The igneous body was intruded at shallow depth, as indicated by the prominent chilled margins of basalt produced by high heat differential between the...