gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1919.018.86.04 On the Origin of Septarian Structure Richardson W. Alfred B.Sc., B.Sc. F.G.S. Lecturer in Civil Engineering, University College, Nottingham 5 1919 18 86 327 338 Copyright © 1919, The Mineralogical Society 1919 Summary

In this paper an endeavour has been made to establish the following points:

That septarian structure consists of a polygonal system of cracks corresponding to a mud desiccation structure.

That the cracking of the nodule is due to the desiccation of a colloidal centre by chemical means.

That the nodules originated by the rhythmic precipitation of solutions diffusing through a colloid according to Liesegang's laws.

Finally, in addition to acknowledgements made in the text, I beg leave to thank Professors H. H. Swinnerton and C. H. Bulleid for help-ful criticism; Mr. H. Preston for placing his collection at my disposal; the chemical staff of University College, Nottingbam, for generous assistance; and Dr. G. T. Prior for his kind attention at the British Museum.