Schreiner and Brown (11) found coallike and charcoallike particles
in all of 34 soils examined by them, and also in samples from a number
of deep subsoils. They point out that numerous forest fires furnish
an ample source of charcoal, but add that it is not known how long
the charcoal persists in the soil. White and Holben (14) showed
that charcoal had persisted in the charcoal plot of the Pennsylvania
experimental plots for more than 68 years. This particular plot
was once the site of a charcoal furnace, and the soil on it now contains
about 4 per cent of carbon. White and Holben found that charcoal
in small quantities was a general constitutent of all the Pennsylvania
plots, and they consider charcoal a general, though small, constituent
of soils in the eastern United States.