The mysterious cliff in China that lays egg-shaped stones

Chan Dan Ya – meaning in Mandarin ‘egg-producing cliff’ – is a 20 metres (65 feet) long and six meters (19 feet) high cliff.  People of the area have observed for years as the eggs ‘incubate’ in hollow overhangs on the cliff and eventually fall to the ground. Each hollow produces one stone egg every 30 years. Local residents collect the spheres because they believe that the “eggs” would bring them good luck.
The rock formed 500 million years ago during the Cambrian period and  the specific section of cliff – part of Mount Gandeng – is made of calcareous rock. Experts say the difference in time it takes for each type of rock to erode has led to the appearance of the “eggs” , which comprise heavy sediment deposits. The “eggs”  are what geologists call concretions. If those concretions are harder than the rock around them (as they often are), they’ll eventually wear down the surrounding rock and break free.