These strange alien-like features are in Nettle Cave, one of the Jenolan Caves. The rounded, pinkish forms are not stalagmites but are life forms known as stromatolites, although the local name is craybacks because they look a bit like crayfish or lobsters. Stromatolites are colonies of primitive blue-green algae that build up in layers by trapping particles of mud and sand. These examples keep wet from the drops of water dripping off the cave ceiling, and receive enough light from the cave entrances to photosynthesize. The green bits are just normal algae. The main stromatolite in the photo is about 1 metre high.
Stromatolites were the most advanced form of life on Earth for 3,500,000,000 years: think about that. They still occur in some shallow marine and lake environments (Shark Bay in Western Australia is the best known), but this is the only example I know of that exists in a cave.
The photo was hand held in very low light conditions.
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