Trace fossil Burrow
Although no details are recorded with this specimen, it is a flint burrow filled with silica that crystalized in the cavity. Flint is composed of silica which originated in the tiny needles that make up the body of sponges. When these simple animals died, their bodies broke up and the needles, or spicules, became buried in sediment. Much later, water percolating through the rocks dissolved the silica and carried it down through the rock layers until it encountered a layer rich with sponges or burrows. The flint bands mark the times when animals flourished on the chalk sea bed, creating lots of burrows.
Find out more on the trace fossils page.