Prehistoric refuse heap. The mounds are largely composed of shells but may contain fragments of animal and bird bones, pottery, and implements of stone and wood. Some burnt wood has been found, as well as burnt stones used as pot-boilers. Sites have been discovered on coastlines throughout the world, including Europe, North and South America, Australia, and Japan.
Middens almost 12 m/39 ft high exist in Florida, USA, but generally the largest mounds are up to 300 m/1,000 ft long, 60 m/200 ft wide and 3 m/10 ft deep, and most examples are much smaller. They are usually the work of Mesolithic (Middle Stone Age) peoples who gathered shellfish in addition to fishing and hunting, but over 600 shell mounds of the Neolithic (New Stone Age) Jōmon period in Japan are known around Tokyo Bay, one dating from the early 2nd millennium BC.
European shell mounds containing oysters, mussels, periwinkles, and cockles are found in the British Isles in Cornwall, Devon, Scotland, and Ireland; and in France, Sardinia, Portugal, and on the coasts of the western Baltic. They were believed to be raised beaches or glacial deposits until 1860, when the Danish zoologist Johannes Steenstrup (1813–1897) noted the variety of remains in the mounds, and that the shells all belonged to well-grown species. The complete absence of gravel in any heap confirmed that they were not a natural occurrence, and he concluded that they were the domestic refuse dumps of a prehistoric people. Steenstrup was an early contributor to the field of archaeozoology. Examination of animal remains did not become routine on archaeological sites until the 1970s.