The action of ice on the shores of the St. Lawrence estuary has been studied since 1964. Shore ice in that area is a powerful agent of erosion and sedimentation. Annually, millions of tons of sediments from clay to boulder size are removed and carried by ice. Erosion of muddy tidal flats and salt marshes is especially significant; a peculiar sedimentary facies results. The St. Lawrence is one of the best sites to study the geologic action of ice because of the presence of (1) relatively large tidal flats, (2) high tidal range and strong tidal current, and (3) ice during a minimum of 4 months.

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