The sandstone was cross-bedded and the individual grains of sand were but poorly cemented together. Underground waters that contained dissolved calcium carbonate circulated through the porous rock with ease and in doing so, deposited calcium carbonate in the open spaces between the sand grains, thereby cementing them together. But instead of proceeding evenly, the precipitation of this natural cement began at a number of scattered points where, perhaps there was a fossil or an extra large grain of sand to serve as a nucleous and it continued outward in all directions from these centers. The result was the formation of a number of spherical bodies of tightly cemented sand grains scattered from the sand stone mass. Had the cementation continued long enough, the spheres would have grown together and the huge rock would have become a homogenous mass. But before this could take place, erosion by wind, rain, wash and running water, began to lower the surface. Of course, the loosely cemented sand was the easiest to carry away, so it went first. The concretions resisted the erosive activity, so were uncovered and left lying on top of the present surface. There are other examples of this phenomena throughout the world, but nowhere are they as unique or as large as they are here. Rock City represents one of a kind in the entire world.
