Calcareous-sileceous matter

Gideon Algernon Mantell, The medals of creation or first lessons in Geology and in the Study of Organic Remains, vol. II, Londres, Henry G. Boh, 1854, p. 559-560.

FOSSIL LARVAE OF PHRYGANEA. Ly. p. 185 The Caddis-worm, so well know to all brethren of the anle, is the larva of the winged insect termed Phryganea , and is abundant at the bottom of fresh-water sreams and lakes; the cases, like those of the marine Sabella (p. 385, fig 6), are always studded over with extraneous bodies, cemented together by a glutinous secretion to the silken integument, or case, which encloses the la(r)va. Some species are coated with pieces of stick or straw, others with minute shells, as planorbis, bithinia, and the like; and when the larvae have passed into the perfect state, their cases, or indusiae, remain.Many of the Tertiary fresh-water limestones of Auvergne are almost wholly composed of the indusiae of Caddis –worms, cemented together by calcareo-siliceous matter, into stone, which is employed for building , and is called indusial limestone (Wond. P. 273) …….