Thanks for the wonderful feedback, guys (and gal). From what I've read, Crosby Street was built up with brick houses and cobblestones in the early 19th century. The asphalt of the adjoining alley has underlying cobblestones too.
Another interesting anecdote, per internet search:
The New York Tribune reported that, in 1877, Mary Flood ran out of a grocery store at 55 Crosby Street pursued by a her husband, James. ''Don't strike me!'' she cried out, but he killed her, thrusting an iron spike deep into her chest. The Floods had ''a very sad reputation for quarreling'' The Tribune said, and lived at 52 Crosby Street; Mrs. Flood, about 30, led a dissolute life, the newspaper said.