Spherical concretions

The spherical concretions from Feleac are sedimentary rock materials
that were cemented together to form a hard structure. The surrounding
sediments slowly erode away, exposing the concretion. They were formed
when calcium carbonate and other cementing minerals precipitated from
the ground water around an organic nucleus, like a shell. Near Feleac
we can find sphere-, and cannonball-shaped concretions.