258 THE POPULAR SCIENCE MONTHLY. . 



selves into two groups, or those relating to plants and animals, which 

 we will consider in their natural order: 



Evidences of Plant-Life. An interesting evidence of the exist- 

 ence of vegetation in Eozoic times is derived from the presence of 

 iron-ores, an argument first set forth by S terry Hunt. The ores are 

 first formed in the hydrated condition, and then lose their water by 

 metamorphic agencies, becoming specular and magnetic, or the state 

 in whi^h the Laurentian irons are now known. Ores of iron are con- 

 ceived to have been formed under similar conditions in all ages. At 

 the present day they accumulate in swamps and low grounds in the 

 condition of the hydrated peroxide (ferric), or bog-ore, oftentimes in 

 company with manganese. The presence of orgauic vegetable matter 

 is requisite in order to extract the iron from the rock or soil and effect 

 its deposition. The metal present in slight amount in the soil is the 

 insoluble ferric oxide, or the familiar condition of iron-rust. Water 

 charged with soluble vegetable infusions, like that in swamps too full 

 of the disagreeable extract of leaves, etc., to be palatable, has the 

 power of dissolving ferric oxide. The process consists in the removal 

 of a part of the oxygen by the vegetable compound, or deoxidation, 

 when the compound becomes changed into the readily-soluble ferreous 

 oxide. But this is not a stable compound in the presence of our at- 

 mosphere. The rejected oxygen is brought back again, and in its 

 recombination takes water with it, producing the hydrated ferric ox- 

 ide, which, being insoluble, is precipitated, and covers the ground on 

 the bottom of the pool. On visiting almost any swamp at the pres- 

 ent day, this reddish-brown coating of hydrated iron-rust may be 

 seen abundantly. Where streams of water cause the swampy water 

 to flow to lower regions, the iron compound is also conveyed in sus- 

 pension, and in the course of a few years a thick deposit of ore is ac- 

 cumulated. Our New England ancestors used these beds for the 

 manufacture of their pig-iron in localities where only the name now 

 exists for the village, such as the Tamworth or Gilmanton Iron-Works. 

 All tradition of the manufacture there has disappeared. The Katah- 

 din Company, in Maine, however, and some others, still derive their 

 ore-supplies from this bog-compound. 



Our theory supposes that the principal iron-ores in every age of 

 the world had their origin in this way. There is no other agent 

 save this organic extract which produces iron-ore on a large scale at 

 the present day ; hence it is rational to explain the origin of ancient 

 ferruginous beds in the same way. If we examine the formations in 

 order, we find the very ores themselves obviously thus accumulated : 

 1. There are the early Tertiary limonite beds of Western New Eng- 

 land, New Jersey, and Pennsylvania, still scarcely removed from the 

 bog form, with the accompanying clays. 2. There are the older Car- 

 boniferous nodules and the celebrated Clinton hematites, differing 

 from the litnoniles only by the absence of water. 3. The specular 



