Calcified algae are important elements of deep-water carbonate sediments in the Cow Head Group. Large algal boundstone boulders in debris-flow conglomerates consist of Girvanella sheets and arborescent clusters of Epiphyton . Silt- and sand-sized particles in fine-grained, thin-bedded slope limestones include abundant Girvanella , as single tubules, rafts of intertwined tubules, oncolites, and intraclasts. Integration of petrographic information from the boulders and fine-grained limestones indicates that many micritic peloids of silt to very fine sand size, the single most abundant particle type in the Cow Head Group, are a combination of comminuted Girvanella tubules and broken Epiphyton rods. Much of the "structure grumeleuse" in intraclasts is also diagenetically modified calcified algae. These findings suggest that many peloids and intraclasts in Early to Middle Paleozoic carbonates, in both shallow and deep water, may have been derived from calcified algae. Calcified algae may have been just as important in producing carbonate sediment during this time as benthic calcified algae are in the modern ocean. The difficulty in recognizing the algal contribution in most ancient sediments is probably caused by the simple microfabric of the resultant grains, filling and obliteration of tubules with micrite cement, or micritization.