In the Geological Magazine for 1918 there appeared three papers discussing the origin of tile system of cracks ill septarian nodules. Dr. A. Morley Davies opened the discussion in a paper where, after a summary of earlier literature, he again put forward an older idea. Without adducing evidence, he considered : (a) that interposition of particles between those of the original matrix caused expansion which set up tensile strain in the growing body ; (b) that the cracking of the nodule was due to the relief of those tensile stresses.