(pronounced "dal," Fr. for a flag-stone or flat tile), a rapid falling over flat smooth rock surfaces in a river bed, especially in rivers flowing between basaltic rocks. The name is common in America, and came into use through the French employes of the Hudson's Bay Company. Well-known "dalles" are on the St Louis, St Croix and Wisconsin rivers. The "dalles" of the Columbia river are very beautiful, and have given its name to Dalles, the county-town of Wasco county, Oregon.