Shingle
Starting just above the high tide mark, the shingle on Omaha Beach consisted of a few yards of smooth stones that had been deposited by the tides. At Dog Green Sector the shingle spanned from the high tide mark to the man-made seawall.
Fact vs. Fiction
Although Captain Miller mentions clearing the shingle just before setting off Bangalore torpedoes to clear the barbed wire on the seawall, nothing that actually resembles the shingle can be seen in the film.