A Bent Pebble

Abstract

ANOTHER explanation may be offered of the origin of the (bent pebble described by Dr. J. S. Lee1. It may represent a worn-out fragment of silicifled sandstone adjoining a right-angle joint junction in the rock. In many places along the Yorkshire coast and elsewhere I have seen somewhat similar angular pebbles obviously derived from septaria-skeletons (melikaria). These septaria-skeletons represent quartzose infillings of the cracks of the septarian nodules, and they are set free by the weathering of the surrounding nodule material. Joints in sandstone are often rimmed by zones of silicified rock which is usually much harder than the original sandstone. On weathering, the softer rock inside the joint blocks is removed first, with the result that the silicified rims are set free. A fragment taken from a knee portion of such a rim could easily have been detached and abraded into a shape resembling the bent pebble. In this case the bending of the pebble would represent an original feature of the rock and would not be due to any subsequent tectonic deformation.