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.
In the past they were often used as construction material.
Comment by Len Hudgens, a geologist:
Concretions, or boulders as we call the large ones are common in the elephant rocks area. Ones in the glaciated areas are called
"erratics" because they were moved and rounded by the glaciers. However, certain rock formations also erode to form concretions or boulders
if there are minerals in the rock that is slightly harder than the surrounding matrix. Iron oxides in sandstone, as in the "Garden of the Gods" area
of southern Illinois, is a good example.