The discovery of striated calcareous concretions in the Gentilly Till supports the hypothesis of an early episode of carbonate precipitation in a glaciolacustrine environment that occurred before the St. Lawrence Lowlands became covered by the last ice advance. Finite 14C ages have been obtained on two such concretions. These ages are in agreement with several others obtained previously on concretions from Lake Deschaillons varves. They suggest a maximum age of ca. 35 000 BP for the Gentilly Till deposition. Inasmuch as the underlying St. Pierre sediments have been dated at ca. 75 000 BP, the St. Lawrence Lowlands would have been ice-free during a large part of the Wisconsinan stage.