Composed of clay

Beck, « Notes on the Geology of Denmark (Beck) », Proceedings of the  Geological Society of  London, Londres, vol. 2, n° 43, 1835.

.. in others districts the formation is composed of clay, which also contains mica, flat masses of hydraulic limestone, like the septaria of the London clay, and occasionally a few organic remains, consisting of scales of fishes apparently belonging to the cyprimadae ; the elytre of beetles, the cases of the larvae of Phryganaea, and an hymenopterous… (il s’agit d’un compte rendu d’une communication ou d’un texte du Dr Beck de Copenhague The Geology of Denmark)