ro, be sure that the underground 
             input temperatures are non-zero and that the pressure 
             thicknesses of the underground layers are non-zero as well.  
               
==========================================================================

 type surf_diff_type

   a public type used to store data needed by the 
       multi-step version of the diffusion algorithm


  real, pointer, dimension(:,:) :: dtmass,    &
                                   dflux_t,   & 
                  