Double diffusive natural convection induced in a vertical porous layer subject to opposing horizontal gradients of heat and mass is studied analytically and numerically using the Darcy model with the Boussinesq approximation. The governing Parameters for the problem are the thermal Rayleigh number, R-T, the Lewis number, Le, the buoyancy ratio, N and the aspect ratio, A, of the enclosure. The analytical solution is developed on the basis of the parallel flow approximation. A numerical study is performed to validate the results of the analytical predictions. It is demonstrated in this study that there exists a domain in (Le, N) plane where, at large R-T, boundary layer profiles are obtained for the velocity and density but not for the temperature and concentration. The boundary layer regimes obtained for this domain (N < 0) are extremely different from those found in the previous studies for the case of aiding buoyancy forces (N > 0).