“Algal Dust” and the Finer-grained Varieties of Carboniferous Limestone

Abstract

Certain of the Lower Carboniferous algae are preserved as moulds in a fine-grained calcareous matrix precipitated by their own life processes. The cell walls of the alga are not preserved. This observation applies to the genera Ortonella, Mitcheldeania, Bevocastria, and Girvanella. In the case of Mitcheldeania the filaments are so close together and so parallel that an impression of a definite wall may be obtained, but occasional irregularities and a comparison of the microstructure with that of other forms leaves no doubt that this too is a precipitate.