Tubular concretions of ferruginous matter, irregularly ramifying through sand, like the roots of trees, are described by Captain Lyon as occurring in Africa.

Lyon's Travels Appendix page 65.) (**Footnote.

Excursions in Madeira 1825 page 139, 140; and Bull.

des Sciences Naturelles volume 4 page 322.) (***Footnote.

Geological Transactions volume 5 page 479.) (****Footnote.