The concretions studied here are actually in the making on the tidal shore of a portion of the Saint Lawrence River. The nuclei around which they form are roots of Scirpus rufus and Juncus balticus var. littoralis . The roots grow vertically in gray-blue clay. The decay of roots causes clay oxidation, the results of which are ochreous cylinders more compact than the original and surrounding clay. The periodic impact of tidal waves releases the concretions from the matrix and the spring tides carry them to the upper part of the shore.