Marcus (Mark) G. Langseth, a pioneer in marine geothermal research, died at his home in Palisades, N.Y., on January 4, 1997, at the age of 64 after a brief illness. He is survived by his wife, Lillian, and two sisters. A memorial service held on January 11 at the Presbyterian Church in Palisades was attended by many of his colleagues, friends, and neighbors. Mark was associated with the Lamont-Doherty Earth Observatory for most of his 40-year career. Beginning as a research assistant and graduate student in the mid-1950s, he became a senior research scientist and an adjunct professor of geology at Columbia University. In 1993 he was appointed to an endowed position as a Palisades Geophysical Institute senior scientist.