The photo records a large stalagmite shawl. A shawl is a limestone formation which has formed by running down the rock, rather than being free-standing like stalactites (which ‘stick tight’ because they hang from the roof) or stalagmites (which grow up from the ground).
Guides to limestone caves usually say that such large lumps of limestone take many thousands—even millions—of years to grow. However, this specimen was found in an abandoned gold mine tunnel near Burrendong Dam in central New South Wales, Australia. This is not far from Stuart Town, the town of ‘The Man from Iron Bark’ in A.B. (‘Banjo’) Paterson’s poem by the same name.
The Australian gold rushes began not far from here at Ophir in 1851, so the tunnel dates after that. Since the tunnel cuts through solid basalt rock, it was probably blasted out with a considerable amount of explosives. Such engineering feats were not undertaken by the average gold rush fossicker and so this tunnel almost certainly dates from considerably later than 1851. In any case, the tunnel and the shawl can be no older than about 140 years.
The horizontal tunnel is about 1.6 metres (about 5 feet) high and runs 50 metres (160 feet) straight into a hill. There are no side-tunnels, so the exploratory tunnel apparently failed to reveal any worthwhile gold-bearing veins. The shawl in the photo is near the inside end of the tunnel—in the middle of the hill.
The lesson? Stalactites and stalagmites do not need a long time to form!