septarian

Updated: July 5, 2026

Something more than a passing look at the coal specimens in a good museum will well repay the time so spent. What are known as septarian nodules, or snake-stones, are, at certain places, common in the carboniferous strata. They are composed of layers of ironstone and sandstone which have segregated around some central object, such as a fern-leaf or a shell.

Edward A. Martin - The Story of a Piece of Coal: What It Is, Whence It Comes, and Whither It Goes