Next, a midden, or kitchen dump, was unearthed, which rested, partially, on top of this walkway. In the fall of 1998 electrical, or soil, resistivity was used to search for underground features. This process involved methodically placing probes in the ground while plotting on a grid any resistance to the electrical current. Soil holds more moisture than, say, a brick wall does, so differences in electrical currents are meaningful and can suggest promising areas for excavation. Generally, soil is characterized archaeologically into distinct layers called horizons.
Ground level is called the A horizon, and is the dark, topsoil layer.
B horizon is subsoil. C horizon in New England is glacial outwash. It wasn't until November 3rd that anyone's trench was taken down through the landfill deep enough to reach the buried A horizon which represents 1897 ground level. This layer was strikingly obvious, however, when it was discovered. The 1897 surface exists today far underground as a 30 - 40cm layer of ash, cinder, and burnt, molten brick and rock.