[Illustration: The Botanic Gardens building is made of limestone.]
This limestone building was built in 1931. Like many of the limestone
buildings in Washington, this building has been cleaned, so it does not
have an accumulation of surface dirt. However, the cleaning and regular
washing by rainfall have accentuated the fossils in the stone, which
dissolve less readily than the calcite matrix. Some of the sculpted
heads above the arches of the building show small black crusts. On the
east side of the building, microorganisms naturally present in the stone
contribute to the deterioration (blackening) of the stone, where water
drips from a joint in the roof.
[Illustration: Fossil details stand out on the limestone at the
Botanic Gardens building; the fossils are more resistant to
dissolution than the calcite matrix that holds the fragments
together.]
The Botanic Gardens Building is the last stop in the Capitol area of
the tour; you may wish, however, to see some bronze alteration on the
Garfield Memorial (First St. and Maryland Ave.) and the accentuated
fossils with surrounding algae or fungi on the limestone posts near
the Capitol Reflecting Pool. The next stop, the Jefferson Memorial, is
about 3.5 kilometers (2.2 miles) from the Capitol.