Anonyme, « Wonderful insects, Insects in Rocks », The World of wonders a record of things wonderful in nature, science and art ,Londres, Cassell, Petter & Galpin, 1883, p. 263.
There is a very thick layer of earth in the centre of France which is composed of countless numbers of the old burrows of caddis-worms. This indusial stone, as it is called, contains so much lime that the layer of earth has become a rock. If a clear shallow brook with a sandy bottom be examined on a summer evening, many small things with heads, eyes, and jaws will be seen struggling about and dragging a kind of sandy, tubular coat which covers them.
The caddis-worms, and many others, collect small stones, grains of sand, and pieces of hard clay, and glue them together in the form of a short tube by means or some sticky stuff which exudes from the skin. The worms live inside these curious coats, and when they die the sandy tube remains .This is called an indusium, and the indusial limestone of France is made up of these remains of ancien caddis-worms. In one of the geological formation of England, which is called the lias, there are layers of earth almost entirely formed by the wing- cases of beetles.