Stromatolites (from Greek strōma, mattress, bed, stratum, and lithos, rock) are layered accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria (commonly known as blue-green algae). Morphology A variety of stromatolite morphologies exist including conical, stratiform, branching, domal, and columnar types. Stromatolites occur widely in the fossil record of the Precambrian, but a… (More on Stromatolite)