boulder clay A glacial deposit that consists of boulders of varying size in a clay-dominated matrix, laid down beneath a valley glacier or ice sheet. Typically it is unstratified and unsorted, and characterized by rock types derived from the country crossed by the depositing glacier. Boulder clay is an older term for what is now more usually known as boulder till.

boulder clay Glacial deposit consisting of boulders of varying size in a clay-dominated matrix, and laid down beneath a valley glacier or ice sheet. Typically it is unstratified and unsorted, and characterized by rock types derived from the country crossed by the depositing glacier. See also TILL.