There are several hundred known shell heaps, along the coast of Maine, some of which have been hardly dug into while others have been completely excavated. Except for their size, they appear much alike both on the surface and in their internal structure.

It is not possible to say with certainty that one tribe or group of Indians inhabited each shell heap from the time of its beginning until the heap reached its present size. It is probable that many of the shell heaps were not, in many instances, occupied year after year, while others show a continual growth without any marked indication of periods when the areas were not in use.