stones below the surface in backyard

We’re finally getting into the garden after three years in our Leffers Manor brownstone. We’ve discovered great masses of round yellow rocks (beautiful) just below the surface of the soil. Makes planting tricky. We’re wondering what these stones could be. Are they part of the natural make-up of the soil? Are they the remains of an old stone wall from days gone by? Thanks for any experience/knowledge you may have.

By Bernie |