Goodman and Cowin (1972) proposed a continuum theory of a dry cohesionless granular material in which the solid volume fraction nu is treated as an independent kinematic field for which an additional balance law of equilibrated forces is postulated. By adopting the Muller-Liu approach to the exploitation of the entropy inequality we show that in a constitutive model containing nu, (nu)over dot, and grad as independent variables results agree with the classical Coleman-Noll approach only provided the Helmholtz free energy does not depend on (nu)over dot, for which the Goodman-Cowin equations are reproduced. This reduced theory is then applied to analyses of steady fully-developed horizontal shearing flow and gravity flows of granular materials down an inclined plane and between vertical parallel plates. It is demonstrated that the equations and numerical results, presented by Passman et al. (1980) are false, and they are corrected. The results show that the dynamical behaviour of these materials is quite different from that of a viscous fluid. In some cases the dilatant shearing layers exist only in the narrow zones near the boundaries.