Floating Islands. An early notice of this phenomenon is recorded in an interesting letter of the younger Pliny to Gallus, in which ho describes the appearance of a number of floating islands in the Lacus Vadimonis, now La-ghetto di Bassano, near Rome. They were covered with reeds and rushes, and the sheep grazing upon the borders of the lake passed upon them to feed, and were often floated away from the shore. On a lake near Gerdauen, in East Prussia, the extent of such islands is said to be sufficient for the pasturage of 100 head of cattle; and on one in Lake Kolm, near Osnabruck, are many fine elms. These islands are produced by accumulations of drift wood, among which drifting sands and earth collect and form a soil, in which plants take root and flourish. The great "rafts" of some of the western rivers are of this nature; for the most part these do not float from place to place, but masses are occasionally detached and drift out from the mouth of the Mississippi, carrying the birds, serpents, and alligators that had taken refuge upon them. Such islands have been seen floating 100 miles off from the mouth of the Ganges, from .which they had been discharged.

On the great rivers of South America they are very often met with, carrying the prolific productions of the vegetable and animal life of the tropics, and depositing them in new localities. Thus they may have been the means of distributing species of the larger animals among the islands of the south Pacific, upon many of which their introduction by any other mode is difficult to account for. Prescott describes the floating gardens or chinampas of Mexico as an archipelago of wandering islands. The primitive Aztecs adopted the plan suggested by these natural objects, and covered rafts of woven reeds and rushes with the fertile sediment drawn up from the lake. Upon these gardens, gradually extending to 200 or 300 feet in length, the Indians cultivated flowers and vegetables for the market of Tenochtitlan. Some of the chinampas were firm enough to sustain small trees and a hut, and could be moved about with a pole or fastened to it at the will of the owner. Remarkable floating islands occur in the Malay archipelago.