Irregularly laminated crenulated surfaces of cyanobacteria of from the shore of the Green River Formation Lake have trapped sediments beneath their surface and the material has been progressively recrystallized. Recrystallization appears to become coarser away from the algal surface. Locally porosity has been filled by calcite coarse calcite spar. The leached fabric of the rock can be identified by the irregular margins to the cavities. Some of these cavities are free of calcite spar. supratidal setting.