code: def mesh(self):
          
          meshes = [surface.mesh for surface in self.surfaces]
          lons = numpy.concatenate([m.lons for m in meshes])
          lats = numpy.concatenate([m.lats for m in meshes])
          depths = numpy.concatenate([m.depths for m in meshes])
          return Mesh(lons, lats, depths)
docs: :returns: mesh corresponding to the whole multi surface