Although the volcanic base of Bermuda is igneous, it is covered by a limestone cap, formed in the Quaternary Period ( the most recent 2.6 million years of Earth's history) by calcium-secreting marine organisms. This formed underwater, but, during ice ages, when sea levels were lower, the limestone broke down into sand. This blew into dunes in which the sand eventually fused back together to form an aeolian (meaning wind blown) sandstone. Coral reefs protect the soft, limestone coastlines from wave-erosion.
Near the posted coordinates there are a few areas in the limestone that have circular bowl shaped depressions. These are called Potholes. A Pothole (or kettle-hole) is a formation caused by a whirlpool eroding a hole into rock. The abrasion is mainly caused by the circular motion of small sediments such as small stones (known as grinders). The interiors of potholes tend to be smooth and regular. An example of this phenomena can be seen on the limestone beds near the waters edge. The objects that form the potholes here are moved by the force of the waves. The grinders do not have to be rocks (we found one example of a bicycle crank assembly), but they are much harder than the softer limestone it is tumbling over. Sometimes the rocks are trapped in a crack or depression and begin swirling in a circular motion, eroding the softer limestone into a round 'pot' hole. And because this erosion activity has been going on for thousands of years, there are perhaps thousands of potholes along the Limestone and Igneous rock shoreline of the island of Bermuda.
