At St. Ludger, Upper Chaudière Valley, in southern Québec, glacio-lacustrine sands of the Gayhurst formation which are older than 20 000 years B.P., are cut by a vertical till dike, 40 cm in width and more than 200 cm in height. The infilling materials are similar to those of the overlying Lennoxville till. The trend of the dike is at right angles to the major direction of flow of the last glacier. It is believed that infilling from above occurred when the Laurentides ice sheet overrode and fractured the underlying sands during the Wisconsin stage.