Shell MiddensShell middens have a special soil chemistry. As shells are dissolved by rainwater that percolates through the soil, they produce an alkaline solution that neutralizes acids given off by forest vegetation. These acids normally destroy bone. Since middens are chemically neutral environments, they are excellent for preserving objects made of bone - which disappear from most sites in less than a century.
Middens are an accumulation of the debris of human activity, so they provide invaluable samples of a region's past environments. In this case, the sample covers a period of over 5,000 years. It supplies information on changes in climate, sea level, and fish and animal species that occurred in the Prince Rupert harbour area.
Shell middens contain layers of dark soil (representing household occupation) isolated by layers of loose shell (representing the refuse that accumulated when the houses were moved to other lots on the site). These layers, or strata, and the tools and bones they contain can be dated using radio-carbon methods. Intrusions into these layers represent activities such as the digging of pits for storage or the placing of a support post for a new house.
Since houses lasted 25 years, on average, the depths here would indicate that as many as 200 houses contributed to the build-up.