[Illustration: DAR—Constitution Hall is made of limestone and was
built in the 1930’s.]
The main damage on this limestone building, built in the 1930’s, is the
blackening of the side balustrade from algae or fungi. The stone is
porous and therefore retains moisture, thus encouraging growth of
organisms. The limestone in this building is quite uniform and shows
little preferential dissolution, except in a few places. On the top of
the balustrade along C Street, for example, some of the calcite matrix
has dissolved from around the fossil fragments, and some holes are
filled with calcite crystals.
[Illustration: Some of the blackening on limestone surfaces may be
from algae or fungi that readily grow in the rough surface in
Washington’s warm, humid climate.]
Continue east along C Street to Memorial Continental Hall.