A continuation of these investigations will perhaps show that our globe has increased gradually from a small beginning to the dimensions it now possesses; that a considerable quantity of the constituents of our sedimentary strata, especially of those that have been deposited in the open sea far from land, are of cosmic origin; and will throw an unexpected light on the origin of the fire-hearths of the volcanoes, and afford a simple explanation of the remarkable resemblance which unmistakably exists between plutonic rocks and meteoric stones.” Such enormous masses of material could well explain the rosy and other curious lights that are from time to time observed. But cosmic dust is not the only matter in the air that could occasion the phenomena; the atmosphere is constantly filled with innumerable forms caught up by currents and carried to inconceivable heights, and thus to great distances, to be precipitated to the earth in hail, snow, or rain. Near St. Domingo, Darwin tells us, the atmosphere became thick and hazy from the impalpable fine dust that actually injured their astronomical instruments. “The morning before we anchored at Porto Praya,” he says, “I collected a little packet of this brown-colored dust, which appeared to have been filtered from the wind by the gauze of the vane at the masthead. Mr. Lyell has also given me four packets of dust which fell on a vessel a few hundred miles northward of these islands. Professor Ehrenberg finds that this dust consists in great part of _infusoria_ with siliceous shields, and of the siliceous tissue of plants. In five little packets which I sent him, he has ascertained no less than sixty-seven different organic forms. The _infusoria_, with the exception of two marine species, are all inhabitants of fresh water. I have found no less than fifteen different accounts of dust having fallen on vessels when far out in the Atlantic. From the direction of the wind whenever it has fallen, and from its having always fallen during those months when the harmattan is known to raise clouds of dust high into the atmosphere, we may feel sure that it all comes from Africa. It is, however, a very singular fact, that, although Professor Ehrenberg knows many species of _infusoria_ peculiar to Africa, he finds none of them in the dust which I sent him; on the other hand, he finds in it two species which hitherto he knows as living only in South America. The dust falls in such quantities as to dirty every thing on board, and to hurt people’s eyes; vessels even have run ashore, owing to the obscurity of the atmosphere. It has often fallen on ships when more than a thousand miles from the coast of Africa, and at points sixteen hundred miles distant in a north and south direction. In some dust which was collected on a vessel three hundred miles from the land, I found particles of stone, above the thousandth of an inch square, mixed with finer matter. After this fact,