been converted into oxide of iron, usually the hydrated form, which is known as brown hematite ore. These deposits are frequently very impure, owing to the commingling of sedimentary material of different kinds, which was often deposited at the time that the iron was chemically precipitated from the water containing it in solution.

Diagrams showing roughly the Mode of Occurrence of Iron Ore in Michigan (Emmons).

The great supply of iron is not drawn from these sources, however, but from the deposits of magnetic and specular ore which are found usually in the so-called metamorphic or crystalline rocks of great age. Whether these were originally great masses of iron pyrites which became subsequently oxidized, or whether they were due to tremendous deposits of iron, originating in much the same way as has been explained, in the remote ages when the rocks, with which they are associated, were formed, is yet in many cases an open question. It would seem, however,⚫ that the latter is very much more frequently the case than the former, as, although often more or less lenticular in form, the ore bodies are usually distinctly interstratified or interbedded. It has also been suggested, owing to the noticeable paucity of iron in the adjacent rocks, that in some way the iron has been leached out of these rocks and segregated in the irregular lenticular masses which we now mine. While it is entirely possible that this may have occurred, it is very difficult of explanation. This much is certain, however, no matter what their origin may have been, they have often, if not always, been very greatly enriched superficially, and in very recent geological times, by the downward percolation of meteoric or surface waters, taking some of the iron contained in the exposed upturned edge of the stratum into solution, and redepositing this iron with the other iron below. In order to do this, they have often effected the process of replacement by substituting the iron for some rock below with which the original deposit was associated, in this way add ing greatly to the purity of the ore. That is to say, in the

extremely gradual process of erosion the surface waters have been for ages constantly dissolving and removing this rock, and depositing in its place the iron which they derived from the upper portions of the iron-bearing stratum. It is simply another example of the process of replacement or substitution already described, and which, as we shall see, has played an important part in forming and enriching many of the metalliferous and other valuable deposits worked by man. The famous Mesabi Range of Minnesota, and mines in other districts in the Lake Superior region, furnish examples where this can be proved to have taken place on a huge scale.

Sometimes these masses of iron ore, especially when contained in the older rocks, are several hundred feet in thickness, and have great longitudinal extension. The ore usually varies from a pure magnetic oxide or magnetite, to what is known as a specular ore, or red hematite, or admixtures of these varieties. The latter (red hematite) is sometimes soft and sometimes hard, but more frequently hard. Often portions of these deposits, and especially deposits of the class to which reference will presently be made, are what is known as brown hematite, or limonite (from leimon, a meadow). Brown hematite ore is the chief ore of the southern United States, and in some cases seems to be due to the oxidation of an original carbonate ore. In the great majority of cases in the southern United States this ore, as well as the socalled "fossiliferous" ore (impure red hematite), is found in rather irregular stratified deposits; but doubtless many of these deposits, like other iron deposits, have been enriched in the way above referred to.

(b.) Deposits of the second class are those where the iron ore is simply and certainly due to the oxidation of original iron pyrites, to which mineral reference has already been made under the head of sulphur. This iron pyrites, when subjected to the oxidizing influence of the atmosphere and of surface waters, loses its sulphur and becomes oxide of iron, that is, ordinary iron ore. This may be a hydrated oxide, or by heat and by pressure, or other causes, the water may have been driven off, leaving it in the form of either magnetic or specular iron ore. A very considerable number of the iron deposits of the world are of this character, out in many, oxidation has proceeded to such a depth that mining 1 It also frequently represents the oxidation of iron pyrites.

has not yet developed the absolutely unaltered iron pyrites, although this mineral often increases in abundance as depth is attained. For example, there is a huge cap of iron ore on the famous deposit of iron pyrites at Rio Tinto, Spain. Examples of this kind are more or less common throughout the Rocky Mountain region. Undoubtedly many deposits of brown hematite, red hematite, and of magnetic iron ore, some of great magnitude, are of this class.1

Iron ore in its legal aspect is interesting, especially in the western United States; for in the eastern portion of the country, as will be seen hereafter, it matters little what the kind of deposit may be, owing to the fact that the common law rules that a man owns where there has been no severance of the mineral estate from the ownership of the soil-all that may be found within his boundary lines extended vertically downward. It has, however, never been judicially decided whether an iron ore deposit valuable for no other metal which it may contain, should be located as a lode or placer deposit when upon government lands. Where it is certainly due to the oxidation of masses of original iron pyrites filling crevices or collected along some line of contact, as between an eruptive rock and limestone, and especially when it carries some other valuable metals, it would certainly seem that, if it is sufficiently continuous, it should be properly located as a lode claim, and not as a placer claim.

The following diagrams will illustrate very roughly the usual manner of occurrence of iron ore and make it more easy to understand the above distinctions.

1 These three ores when chemically pure- that is, when the iron contained in them is united only with oxygen, which purity is never met with can respectively contain 59.8, 70, and 72.4 per cent of

metallic iron. It is very high grade ore of either class that shows a percentage six or seven units less than the possibilities mentioned.

Occurrence of more or less Stratified and Pockety -or Irregular- Iron Ore
Deposits.

Mode of Occurrence of Contact Iron Ore Deposits which are certainly due to the Oxidation of Iron Pyrites.

Manganese.

The principal use of this quite important metal is

in the manufacture of steel.

It is derived principally from two ores,-oxide of manganese and carbonate of manganese. These ores, especially the former, occur quite abundantly in nature, although nothing like to the same extent as iron.

The chief supply of manganese is drawn from perfectly stratified sedimentary beds, as in Chile, Russia, Cuba, etc., although in the United States its occurrence is very much more pockety. In this country it is chiefly found in beds of clay resulting from the disintegration of some certain kind of rock, which may be either original sandstone, as in Virginia, or limestone, as in Arkansas. It is chiefly found in irregular masses varying from less than an ounce to many tons in weight. There is, however, every reason to believe that the manganese was in the original rock which has dissolved into clay; that is to say, when this rock rotted into clay the manganese ore remained in the latter in some cases in somewhat the same position as it was originally deposited in the sedimentary material which was afterward consolidated into hard

rock. But it is much more probable, in the majority of cases, that what has been referred to as the process of superficial enrichment may have taken place in the majority of these deposits in somewhat the same manner as in the iron ore deposits which have already been described, so that these nodular masses of manganese ore in the clay represent the segregation of this material, the rock which originally contained it having contained it in a much more disseminated condition. These masses are therefore much larger and more abundant than they would have been otherwise.1

The ore is usually confined to a certain stratum or certain strata in a series of sedimentary rocks, and it adheres to these strata with great pertinacity. This is simply due to the fact that the conditions for the deposition or precipitation of manganese ore were present when these particular sediments were deposited, and were not present when either the older or younger sediments were deposited. Whether the ore was originally deposited in the form of a carbonate or as an oxide is not proven, though many think that, as in the case of some iron ores, it was originally deposited in the form of a carbonate and has been subsequently changed to an oxide. This, however, is of small importance here.

The other class of deposits are carbonate and silicate of manganese. The latter has never been used as a manganese ore, although it is quite common in our western United States, where it often marks the outcrops of fissure veins, having been oxidized superficially to the common black oxide of manganese. It is usually very impure. The deposits of carbonate of manganese are beginning to attract attention. For example, in the 1 The peculiar mammillated or rounded appearance of these nodules lends force to this theory.