1378. The compound modifications are, 6. Cumulo-stratus, or twain cloud; the cirrostratus blended with the cumulus, and either appearing intermixed with the heaps of the latter, or superadding a wide-spread structure to its base (f); 7. Cumulo-cirro-stratus, or Nimbus; the rain-cloud, a cloud or system of clouds from which rain is falling. It is a horizontal sheet, above which the cirrus spreads, while the cumulus enters it laterally and from beneath (g g); 8. The Fall Cloud, resting apparently on the surface of the ground (h).