In repairing the modern road just outside the south entrance to the tunnel, a stratum of carbonized corn, beans, &c., and a quantity of burnt wood, stones, tiles, pottery, &c., was found under and above the modern road, for a distance of some Soo yds.
It has been found useful in some cases to examine microscopically the thin film of coal that often covers the pinnae of fossil fronds, in order to determine the form of the epidermal cells which may be preserved in the carbonized cuticle; rectilinear epidermal cell-walls are usually considered characteristic of Cycads, while cells with undulating walls are more likely to belong to Ferns.
In the stairs; while the objects found in them - household pottery, &c. - and near them (in some cases silos containing carbonized grain and dolia) point to the same conclusion.
It reacts most energetically with many organic compounds, removing the elements of water in many cases and leaving a carbonized mass.
The disadvantage in this process is that the by-products, such as pyroligneous acid, acetone, wood spirit, &c., are lost; as an alternative method, wood is frequently carbonized in ovens or retorts and the volatile products are condensed and utilized.