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224 serve as rullocks for ethereal rowers to navigate this brilliant gondola." In Thames water, Naviculæ exist in great abundance, the most common form being that of an Indian canoe, with a gracefully curved prow.

The flint which forms the skeleton of the diatom, and the armour of the animalcule, is withdrawn from its solution in the waters inhabited by these minute organisms by some mysterious operation of the vital force. So prolific are these tiny forms of life, that it has been estimated that a single animalcule can increase to such an extent during one month, that its entire descendants can form a bed of silica or flint twenty-five square miles in extent, and one foot and three-quarters thick! "As a parallel to Archimedes," says Bischof, "who declared he could move the earth if he had a lever long enough, we may say:—Give us a mailed animalcule, and with it we will in a short time separate all the carbonate of lime and silica from the ocean!"

This leads us to consider more minutely the part played by the animals and plants of the invisible world in the formation of the beds of rock which form the solid crust of our globe. Twenty years ago Professor Ehrenberg discovered a wonderful bed of earth which was almost entirely composed of living infusoria, and which extended to twenty, and, in some localities, even to sixty feet in depth. This formation is situated in Berlin, at a depth of