  A new, da Vinci, fluid is described as a model for flow of dense granular
matter. We postulate local properties of the fluid, which are generically
different from ordinary fluids in that energy is dissipated by solid friction.
We present the equation of flow of such a fluid and show that it gives rise to
formation and growth of plug flow regions, which is characteristic of flow of
granular matter. Simple explicit examples are presented to illustrate the
evolution of plug flow regions.
