Sites on the tour: 1. THE CAPITOL BUILDING 2. THE PEACE MONUMENT 3. THE GRANT MEMORIAL 4. BOTANIC GARDENS BUILDING 5. JEFFERSON MEMORIAL 6. LINCOLN MEMORIAL 7. CAPITOL GATEHOUSE 8. ORGANIZATION OF AMERICAN STATES BUILDING 9. DAR—CONSTITUTION HALL 10. DAR—MEMORIAL CONTINENTAL HALL 11. CORCORAN BUILDING 12. RENWICK GALLERY 13. FEDERAL TRIANGLE BUILDINGS 14. WASHINGTON MONUMENT Continue south along First Street to the Grant Memorial on your right. The Grant Memorial—Site 3 [Illustration: The Grant Memorial consists of bronze statues on marble bases; although the statues were cleaned, the staining on the marble remains.] This memorial, dedicated in 1922, consists of a group of bronze sculptures mounted on marble bases. Bronze weathers outdoors if it is not cleaned and waxed regularly. Like stone, bronze dissolves where it is exposed to rainfall, developing a green color and a pitted surface, and it also alters in sheltered areas, with accumulation of a blackened layer. The most notable stone deterioration visible here is the green stain on the marble bases, caused by runoff from the weathered bronze. The green stain does not damage the marble, but it is unattractive, and there are no methods currently available to remove the stain without damaging the marble. [Illustration: The light-green color on the bronze statues at the Grant Memorial is typical of the way bronze weathers when it is exposed to acidic rain; the rain dissolves some of the metal and causes staining of the white marble bases.] Continue south, crossing Maryland Avenue, to the Botanic Gardens. Botanic Gardens Building—Site 4 [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.]