Experiments show that gravity-driven dry granular flows are essentially layered for smooth spheres. This paper describes layer-to-layer interaction in the flow. Assuming two-dimensional flow and neglecting the interaction of grains within the same layer, one may idealize the problem as an elastic sphere under external forces moving down an incline within a layer of identical spheres placed equally apart. The moving sphere is thus subjected to the total gravitational force which includes the weight of a specified number of layers of spheres above it and its own weight. With such a mechanical approach, estimates can be made for the magnitudes of collisional and non-collisional stresses.