STOP 6: CALVERT STREET MONUMENTS - Battle of North Point Monument and Monument to Negro Heros of the United States - Calvert and Fayette Streets

       From the corner of Redwood and Calvert Streets, walk north on Calvert Street for two blocks to Fayette Street. Calvert Street is divided here and Stop 6 is on the “island” in mid-street (Figure 6a).

     The stone wall (Figure 6b) around the Battle of North Point Monument is Cockeysville Marble, a building stone quarried in Baltimore County, Maryland. The Cockeysville Marble is a metamorphic rock of Precambrian age, about 600 million years old. Originally a limestone, it was transformed by heat and pressure into marble. The term meta-limestone also describes this marble, meaning that it was a limestone changed by metamorphism. The main minerals in marble are calcite (CaCO3) (just as in limestone) and dolomite [CaMg(CO3)2]. Fossils have not been found in this marble, however, if there had been any fossils in the original limestone, it is likely that metamorphism would have destroyed them. Crystal size ranges from fine grained to coarse and sugary.

     Cockeysville marble is mainly white although some layers can be gray or pink. Where the building stone surfaces are kept cleaned and polished the marble generally remains white; where dust accumulates or impurities in the stone weather, the marble may become a dove-colored gray. Like limestones, however, marbles can occur in a wide array of colors.Cockeysville Marble was used in building the United States Capitol, the majority of the Washington Monument in Washington, D.C., and the Washington Monument in Baltimore, located a few blocks north of the Inner Harbor area. Cockeysville Marble has also been used to form door steps and sills in residential Baltimore.

      Walk around to the north side of the monument and into the small park. The benches and walls in this area are made up of a Georgia gneiss (building stone trade name “Tidal Gray Granite”) which was quarried near Elberton, Georgia (source: Maryland Stone Service) (Figure 6c). This is a metamorphic rock with obvious foliation, which is a banding or layering of minerals. The dark minerals in this gneiss are biotite mica and hornblende; the light minerals are feldspar and quartz. The parent or original rock was probably an igneous rock, such as a granite. The original rock was metamorphosed (changed) during an orogeny (mountain-building event) when the resulting heat and pressure caused partial melting and segregation of the minerals. The banded appearance developed when minerals grouped on the basis of different densities.

     Notice the bench on the east side that has been repaired with a granite slab. This provides an excellent comparison of the two classes of rock: igneous (the granite) and metamorphic (the gneiss).

     Another type of stone seen at the north end of the park forms the base of the Monument to Negro Heroes of the United States (Figure 6d). This is a dark gray, fine-grained granite (Figure 6e) from Canada. The color is due to the glassy, gray grains of quartz mixed with the white feldspar and a scattering of very small crystals of black biotite mica.