Examination of a marine algal deposit from the Champlain Sea (10 800 ± 150 y old) found by Mott (1968) revealed that it is composed mainly of well preserved blades of Laminaria. These were associated with another brown species not susceptible of definite identification and a single fragment of a foliose red species, probably Rhodymenia.Filaments of Audouinella membranacea were found in hydroids in the deposit and another small red alga, Acrochaetium identified. The presence of several plant pigments was indicated by chromatographic and spectrographic techniques.