Pictured above is a good example of cone in cone structure. It’s a common feature in limestone, although it can form in other rock types as well. This sample was collected from the DeQueen Limestone of the Gulf Coastal Plain of southern Arkansas.
From the picture, you can see that cone in cone structure results in numerous nested cones, which resemble Bugles Corn Snacks (product placement). The craters, visible above, are places where cones have worked themselves out of the rock. In other places you can see the round bottom of a cone: those cones have yet to work free from the rock.
Thus far, no one is certain how cone in cone structure forms. Several theories have been offered, but scientists have yet to arrive at a consensus. However it forms, it’s fascinating to look at and wonder about!