Hudson, J. D.: Algal limestones with pseudomorphs after gypsum from the Middle Jurassic of Scotland.Lethaia, Vol. 3, pp. 11–40. Oslo, January 15th, 1970.Algal limestones from two horizons within the Great Estuarine Series of the Hebrides are described. That from the Mytilus Shales is a typically stromatolitic limestone formed by algal trapping and binding of micrite pellets. Calcite pseudomorphs after gypsum occur along some of the laminae. The limestones from the Lower Ostrea Beds include less regularly‐stromatolitic types, and nodular algal limestones that contain tubes of calcified algae, notablyCayeuxia nodosaAnderson. The algal nodules also yield uncalcified tubes composed of organic material, that are comparable to recentSchizothrix.These algae form inter‐growths similar to those recorded from the recent supratidal deposits of the Bahamas. The algal nodules are often coated with microtufa. Pellet‐ and spheru‐lite‐limestones are associated with the algae, and pseudomorphs after gypsum are again found. Isotopic data on the carbonate‐carbon, and the palaeoecological implications of the algae and the pseudomorphs