This is a blending of two kinds of cloud (hence the name of _twain-cloud_,) and it often presents a grand and beautiful appearance, being a collection of large fleecy clouds overhanging a flat stratum or base. When a cumulus increases rapidly a cumulo-stratus frequently forms around its summit, resting thereon as on a mountain, while the former cloud continues to be seen, in some degree, through it. This state of things does not continue long. The cumulo-stratus speedily becomes denser and spreads, while the upper part of the cumulus extends likewise, and passes into it, the base continuing as it was. A large, lofty, dense cloud is thus formed which may be compared to a mushroom with a very thick, short stem. The cumulo-stratus, when well formed and seen singly, and in profile, is quite as beautiful an object as the cumulus. Mr. Howard has occasionally seen specimens constructed almost as finely as a Corinthian capital; the summit throwing a well-defined shadow upon the parts beneath. It is sometimes built up to a great height. The finest examples occur between the first appearance of the fleecy cumuli and the commencement of rain, while the lower atmosphere is comparatively dry, and during the approach of thunder storms. The appearance of the cumulo-stratus, among ranges of hills, presents some interesting phenomena. It appears like a curtain dropping among them and enveloping their summits; the hills reminding the spectator of the massy Egyptian columns which support the flat-roofed temples of Thebes. But when a whole sky is crowded with these clouds, and the cumulus rises behind them, and is seen through the interstices, the whole, as it passes off in the distant horizon, presents to the fancy mountains covered with snow, intersected with darker ridges, lakes of water, rocks and towers. Shakspeare seems to have referred to this modification in the well-known lines:— “Sometimes we see a cloud that’s dragonish; A vapour, sometimes, like a bear or lion, A towered citadel, a pendent rock, A forked mountain, a blue promontory, With trees upon ’t that nod unto the world, And mock our eyes with air.— That which is now a horse, even with a thought The rack dislimns, and makes it indistinct As water is in water. The _distinct_ cumulo-stratus is formed in the interval between the first appearance of the fleecy _cumulus_ and the commencement of rain, while the lower atmosphere is yet dry; also during the approach of thunder storms when it has frequently a reddish appearance. Its _indistinct_ appearance is chiefly in the longer or shorter intervals of showers of rain, snow, or hail. THE CUMULO-CIRRO-STRATUS; NIMBUS OR RAIN-CLOUD.