Slightly acidic rain water combined with carbon dioxide in the air, forming carbonic acid in the trapped sand. Over time, the acid dissolved the calcium carbonate that held the sandstone together, slowly wearing away the rock until openings were formed. In other fins, an exposed layer of weaker rock lay beneath a stronger one.
Wallerian degeneration is nothing but a well organized morphological and biochemical change that results in axons, microphases distal to the site of injury and degenerates those sites. It is some what a cascade of cellular and molecular events.
