Numerical experiments on the initial formation, growth, and merging of convective layers in a density stratified solute solution contained in a narrow slot with steadily applied lateral temperature gradient are reported on. At supercritical conditions, the kinetic energy of the layers, once formed, steadily increases until viscous interaction leads to the eventual merging of adjacent layers. The stability of the initial layer formation is studied. The critical thermal Rayleigh number for neutral conditions is determined through numerical experiment in close agreement with previous linear analysis and experimental results.