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236 in their remains of plant-life, are no less trustworthy proofs of its existence. They are themselves largely the result of vegetation in some form. Dr. Hunt originally explained this connection, illustrating it by identical processes in the world about us. If the reader visits a bog-land in summer, where slowly-running or stagnant water collects in pools, or if he stands upon the edge of a morass or marsh, he will notice angular, iridescent films floating upon the surface. They are thin pellicles of iron oxide, which will soon break up and sink, to be succeeded by fresh "skins," which in turn disappear, building up a growing layer of bog-iron ore beneath the water. The theory is simple. Iron exists under two forms, a soluble or monoxide, and an insoluble or sesquioxide. The latter is widely disseminated through the rocks and soils. The insoluble modification is reduced to the monoxide or soluble state in the presence of finely divided and rotting vegetable matter, or in water charged with vegetable infusions, as emacerated leaves and tissues. Rains and streams carry it away to lowlands and depressions, where it becomes, through contact with the air, again oxidized or rendered insoluble, and is redeposited in streaks and bands. The widespread action of vegetable acids is here concerned. Humic, crenic, apocrenic, and related acids, in conjunction with the reducing power of carbonaceous residues, removed iron oxide from the original rocks, and through the agency of water gathered it—useless as long as it remained scattered in minute particles through vast terrains—into enormous masses, the source and maintenance of our industries, thus garnered through these gentle and silent methods. Such has been the growth of the large deposits in the Marquette region, in the Adirondacks, and at Pilot Knob—deposits which under the influence of heat have become changed into the specular ores, the magnetites, and hematites. They point unmistakably to the existence of plants, and no less to their duration over immense periods of years.

The proofs of animal life are less satisfactory, and have been discredited in high scientific writings, or, more accurately, the morphological types of that life have been rejected, leaving the general presumption unquestioned that animal life of some kind prevailed. In the first place, the phosphatic minerals found in the archæan rocks are considered derivative from organic remains, as to-day phosphorus as a phosphate results from animal secretions, though phosphorus is omnipresent in the plant-world, and the ashes of various vegetables yield from eight per cent, to fifty-three per cent, of phosphoric acid, while the annual shipment of flour and wheat from our shores represents thousands of tons of this element. In this respect the evidence does not seem altogether controlling that these archæan phosphates necessarily resulted from animal débris. But the argument rests upon surer grounds. In 1868, Logan, Dawson, Carpenter, and Hunt, prepared a paper of great merit upon an archæan fossil, which they named Eozoön, and which they considered representative of the zoölogical sub-