During the year 1878 masses of floating pumice were reported as existing in the vicinity of the Solomon Isles, and covering the surface of the sea to such extent that it took ships three days to force their way through them. Sometimes these masses of pumice accumulate in such quantities along coasts that it is difficult to determine the position of the shore within a mile or two, as we may land and walk about on the great floating raft of pumice. Now, recent deep-sea soundings, carried on in the 'Challenger' and other vessels, have shown that the bottom of the deepest portion of the ocean, far away from the land, is covered with these volcanic materials which have been carried through the air or floated on the surface of the ocean. To these deeper parts of the ocean no sediments carried down by the rivers are borne, and the remains of calcareous organisms are, in these abysses, soon dissolved; under such conditions, therefore, almost the only material accumulating on the sea bottom is the ubiquitous wind- and wave-borne volcanic products. These particles of volcanic dust and fragments of pumice by their disintegration give rise to a clayey material, and the oxidation of the magnetite, which all lavas contain, communicates to the mass a reddish tint. This appears to be the true origin of those masses of 'red-clay' which, according to recent researches, are found to cover all the deeper parts of the ocean, but which probably attain to no great thickness. But while some portion of the materials ejected from volcanoes may thus be carried by winds and waves, so as to be dispersed over every part of the land and the ocean-bed, another, and in most cases by far the largest, portion of these ejections falls around the volcanic vent itself. It is by the constant accumulation of these ejected materials that such great mountain masses as Etna, Teneriffe, Fusiyama, and Chimborazo have been gradually built up around centres of volcanic action. There are cases in which the formation of volcanic mountains on a small scale has actually been observed by trustworthy witnesses. There are other cases in which volcanic mountains of larger size can be shown to have increased in height and bulk by the fall upon their sides and summits of fragmentary materials ejected from the volcanic vent. In all cases the examination of these mountain-masses leads to the conclusion that they are entirely built up of just such materials as we constantly see thrown out of volcanoes during eruption. [Sidenote: FORMATION OF VOLCANIC MOUNTAINS.] Thus we are led to the conclusion that all volcanic mountains are nothing but heaps of materials ejected from fissures in the earth's crust, the smaller ones having been formed during a single volcanic outburst, the larger ones being the result of repeated eruptions from the same orifice which may, in some cases, have continued in action for tens or hundreds of thousands of years.