From the indestructible nature of their flinty coverings the Diatoms play a no less conspicuous part in the geological history of our globe than the calcareous Foraminifera.
Extensive rocky strata, chains of hills, beds of marl—once deposited at the bottom of the ocean, and raised by subsequent changes of level from the depth of the waters—contain the remains of these little plants in greater or less abundance. No country is destitute of such monuments, and in some they constitute the leading features in the structure of the soil. Under the whole city of Richmond, in Virginia, and far beyond its limits, over an area of unknown extent, they form a stratum of eighteen feet in thickness, and similar deposits are found to alternate in the neighbourhood of the Mediterranean with calcareous strata chiefly composed of Foraminifera. At first sight it may seem a gross exaggeration to attribute so vast an agency to beings individually so minute, but when we recollect how quickly they multiply by division, and how their activity dates from the first dawn of organic creation, their architectural powers no longer seem incredible. In forty-eight hours a single diatom may multiply to 8,000,000, and in four days to 140,000,000,000,000, when the silicious coverings of its enormous progeny will already suffice to fill up a space of two cubic feet. No wonder, then, that during the course of ages these microscopic plants have been able to form prodigious strata wherever circumstances favoured their propagation. In no case is the power of numbers more forcibly exemplified, for where can we find results more vast, proceeding from the infinite multiplication of the smallest individuals, than that whole tracts of country should literally be built up of the skeletons of Foraminifera and Diatomaceæ?
Hooded Merganser.
[CHAP. XX.]
THE GEOGRAPHICAL DISTRIBUTION OF MARINE LIFE.
The Dependence of all created Beings upon Space and Time.—The Influences which regulate the Distribution of Marine Life.—The four Bathymetrical Zones of Marine Life on the British Coasts, according to the late Professor Edward Forbes of Edinburgh.—Abyssal Animals.—Bathybius Haeckelii.—Deep-Sea Sponges and Shell-Fish.—Vivid Phosphorescence of Deep-Sea Animals.—Deep-Sea Shark Fishery.—The "Challenger."
The wanderer to distant lands sees himself gradually surrounded by a new world of animals and plants. On crossing the Alps, for instance, the well-known vegetable forms of our native country leave us one after the other; the beech, the fir, the oak, no longer meet the eye, or appear but rarely, and of more stunted growth, while in their stead citron and olive-trees decorate the landscape; and finally, on the shores of the Mediterranean the world of palms begins to disclose its beauties.