Doug, you are correct, the Princess Margaret Rose Caves on the Sa Vic Border.
Over to you.
History and Formations
The Cave
Mr K. McEachern and Mr J. Hutchesson and his sons Alan & Bernie, first explored the cave in 1936.The original entrance was a 17m vertical shaft, as visitor access was restricted a stairwell had to be dug through the limestone, this stairwell took Keith and Bunny 5 years to dig. They developed the cave as a tourist attraction with Bunny" Hutchesson acting as the first permanent guide, conducting tours from 4th January 1941. Since 1980, the cave has been part of the Lower Glenelg National Park.
Formations
Most limestone caves are formed by water seeping down through cracks and fault lines in the limestone, dissolving the rock and creating fissures and tunnels. The formation of Princess Margaret Rose Cave, however, was assisted by water from the Glenelg River which worked its way along a fault line for approx 500m. This occurred above its present height. The water scalloped the walls of the cave and wore a reasonably level floor.
Rainwater, as it seeps from the surface, acts as a weak acid to dissolve the limestone, producing a solution of calcium bicarbonate. When this reaches the air of the cave, carbon dioxide is released and calcium carbonate is deposited in the form of calcite crystals.
These crystals make up the diverse and spectacular formations of the cave. The different colours are caused by tannins and minerals washed down by rainwater from overlying soil.