Upward-thinning stellate and polygonal carbonate structures are compared to modern and ancient stromatolites. Although tufted microbial mats are common in modern settings they have rarely been described from ancient rocks owing to their poor preservation potential. The preservation of these from the Stoer Group is due to early replacement by calcite before their original tufted relief could be obliterated by compaction. Associated limestones are interpreted as flat to mamillated microbial mats.--Modified journal abstract.