Drift ice has a double effect in tidal marshes along the eastern shore of James Bay (51°09' - 54°37' Lat. N.). First, they cut off most stems, scratch the vegetated and soil surface digging long furrows and shallow circular depressions, and tear away peat blocks producing depressions, 15 to 30 cm in depth, and of various forms and sizes. Secondly, at breakup, they left at the surface of marshes a large amount of coarse detrital material ranging from the size of large boulders, often exceeding 200 cm in diameter, to the size of fines, including sand and gravel, and peat blocks. Generally speaking, the morpho-sedimentological aspects of tidal marshes are strongly modified by drift ice, which controls their ecology and allows one to classify them into the category defined as "cold regions tidal marshes".