Lake Ontario is divided by two ridges of glacial till into three basins — Niagara, Mississauga, and Rochester in the western, central, and eastern parts, respectively, of the lake. Piston and benthos cores were taken by the Canada Centre for Inland Waters from each of the three basins from the research ship CSS Lymnos. The lithology, mineralogy, pollen content, and magnetic parameters of the sediment in these cores have been studied as a means of chronostratigraphic correlation. The transition from late glacial to postglacial sediment is inferred to take place where there is a marked increase in the numbers of pollen in the cores. Further chronostratigraphic correlation between cores has been based mainly on simultaneous matching of the magnetic parameters of declination, inclination, intensity, and ratio of natural remanent magnetization (NRM) to anhysteretic remanent magnetization (ARM). Type curves of declination, inclination, and NRM/ARM for Lake Ontario have been produced.