Tuckahoe was built on marble — the pale stone came out of these hillsides and went off to become buildings elsewhere, and the ledge still shoulders up under the lawns on the steeper streets. GREEN GRASS LANDSCAPING & MASONRY INC. mows and maintains those sloped, terraced yards, the kind that ask for a careful line and a steady hand. Late in the day, when the sun drops behind the ridge toward Bronxville, the grass goes deep green and holds it. Cleanups open the growing year in spring and close it out once the leaves let go. Between them, a summer of level cuts and clean borders on a hill that never quite lies flat.