[Illustration: Memorial Continental Hall, built in 1909, is part of
the Daughters of the American Revolution building complex.]
[Illustration: Carvings at the base of the columns on the south side
of Memorial Continental Hall show that carved details and sharp
edges remain on sheltered areas.]
The porch area on the south side of this marble building built in 1909
is a good place to look at some contrasts in marble deterioration. Parts
of the balustrade have been replaced, as shown by differences in color
and surface roughness of the stone. The exposed stone surface along the
top of the balustrade is rougher than the surfaces in more sheltered
areas. The columns on this porch are carved around the base, so you can
examine the effects of exposure to rain on the carving details. The more
exposed carvings have lost their sharp edges and definition compared to
the sheltered carvings. The bases of the columns contain small amounts
of pyrite, which is more resistant to weathering than is the calcite in
the marble surrounding the pyrite. The sheltered part of the window-sill
support on the west side of the porch shows an alteration crust, a dull
gray accumulation on the stone surface.
[Illustration: On an exposed portion of the carving on the columns
at Memorial Continental Hall, the edges of the marble have rounded
and the surface has roughened.]
[Illustration: Pyrite grains stand in relief where calcite and micas
have weathered out of the marble at Memorial Continental Hall.]
[Illustration: A dull gray surface on the marble on the window-sill
support shows where an alteration crust is just beginning to
develop.]
At the corner of 17th and C Streets, turn left and walk north along
17th Street. On our way to the Corcoran Gallery, we will pass the Red
Cross building (marble, 1917). Some of the same types of marble
deterioration observed at other locations are also present here.