FLOATING ISLANDS, islands formed either•by the aggregation of driftwood in rivers and the deposition thereon of soil and vege table matter, or by the detachment of portions of a river bank or lake shore. Tall trees are sometimes seen standing erect on such islands as they are carried down by the river current. Floating islands are sometimes seen 50 or 100 miles distant from the mouth of the large rivers of America, Asia and Africa. Portions of the alluvial soil from river-deltas, held together by the roots of mangroves and other trees, are sometimes detached by hurricanes or typhoons and then swept out to sea; such islands have been met with in the Philippines, in the seas of the East Indies and in the'Pacific. A floating island is mentioned by Herodotus as existing in Egypt. In that country Mocks of jungle growth composed in part of masses of papyrus, called -mid, obstruct the river, and have been known to stop entirely the navigation of the White Nile. They are so firmly compressed by the force of the current that men can walk over them. Some of these blocks or floating islands removed in 1902 were a mile long and 20 feet thick. Floating islands were known to Roman writers. Those on Lake Vandimona were, according to the younger Pliny, capable of supporting sheep. Loch Lomond in Scot land long possessed a floating island, which has now, however, disappeared or become attached to one of the stationary islands of the. loch. In Ireland large masses of peat float about some of the bogs. In England, in Lake Der wentwater, there is an instance of. nit island which appears and disappears from time to time in the same spot. Perhaps the most sat isfactory of the many theories which have been proposed to account for this phenomenon is that which attributes its rising from the bot tom of the lake, where it ordinarily rests, to the permeation of its mass by marsh-gas during hot weather, the upward motion being assisted by the growth of bouyant water-plants on its surface. Between 1696 and 1829, similar islands
were observed at irregular intervals, generally, however, after great droughts and violent storms, in Lake 'Wang in the Swedish province of Smiland. Oceanic floating islands some times perform important service in the trans portation of vegetable seeds from place to place, also in the distribution of animal species, by carrying insecttland- moihnica and snail mam malia, more rarely reptiles. Darwin with islands floating on Lake Tagua-Cagua in Chile which passed from side to side of the lake and carried cattle and horses as passengers. In northern India and on the borders of Tibet and in Persia, floating gardens are often erected by the natives for the purpose of raising melons, cucumbers and other similar vegetables and plants, which require a very aqueous soil for their cultivation. These gardens, however, are of a very fragile nature, and rarely -exceed a foot in depth of soil, their prime structure being composed of wicker-work, interlaced with reeds and wattles and covered with mat ting, over which the earth is placed. In the Vale of Cashmere the lakes contain floating gardens devoted to the same purpose but these are in reality portions of the marshy ground made.to float artificially by cutting through the roots of the reeds and other plants about two feet below the surface. The Chinese, too, de vote considerable attention to this style of hor ticulture, but more by way of ornamentation. Floating gardens, or chinampas, also existed in Mexico before the Spanish conquest. Clavi gero describes them as formed of wicker-work, the stems of water-plants, and mud, the largest sometimes having on them a tree or a hut. Both flowers and vegetables were grown on them.
a variety of opal, or hydrated silica, occurring in concretionary masses of such a porous texture that they float on water. They are of a gray or white color, break with uneven fracture and sometimes have a hard nucleus of flinty appearance.