The very extensive pumice deposits at Neuwied and the lava and other volcanic rocks belong to a more recent epoch.
In 1886 there was a serious volcanic eruption in the outlying island of Nivafoou, and at the same time Falcon Reef, normally awash at high water, discharged sufficient scoriae and pumice to form a new island 50 ft.
The residual gas is then passed through a tube containing porous materials, such as woodor bone-charcoal, platinized pumice or spongy platinum, then mixed with steam and again forced through the tube.
Lumps of manganese oxide, with a black, shining outer surface, are also characteristic of this deposit, and frequently encrust pieces of pumice or animal remains.
Lava is much used for paving-stones in the neighborhood of volcanic districts, where pozzolana (for cement) and pumice stone are also important.
Millstones and pumice were also exported, but for the former the more gritty lava of Rocca Monfina was later on preferred.
Almost every temple had its fetish stone on a level with the pumice stone, which is the Poseidon of the Mangaians.
The lagoon is slowly filling up and becoming cultivable land, but the rate of recovery from the sea has been specially marked since the eruption of Krakatoa, the pumice from which was washed on to it in enormous quantity, so that the lagoon advanced its shores from 20 to 30 yards.
Broken as is the surface, poor as is the soil of certain tracts, there is but little of the island which will not ultimately be cultivated with profit as pumice and clay-marl yield to labour.
The dredge often brings up large numbers of nodules formed upon sharks' teeth, the ear-bones of whales or turtles or small fragments of pumice or other volcanic ejecta, and all more or less incrusted with manganese oxide until the nodules vary in size from that of a potato to that of a man's head.