oils a good opportunity to escape. When the rocks, however, are lying level it is impossible to tell where it will be found, except to say generally that if found at all it is likely to be met with in certain oil-bearing strata. The random drilling of exploratory holes is the only way to test such a region. The depths at which it is found in this country usually vary from five or six hundred feet to very often upward of three thousand feet. The sinking of a new oil well in a so-called "pool" often interferes with the production of a previously existing well in close proximity to it. These so-called pools in the oil-bearing sandstones or so-called "sands" are simply localized areas of oil-bearing territory in certain and, by experience, well-recognized strata, usually sandstones or grits, as in Pennsylvania and California. They may be found, however, in the fossiliferous strata of any age, from Silurian (in Ohio) to Devonian, Sub-carboniferous and Carboniferous in Canada, Pennsylvania, West Virginia, etc.; Tertiary in Russia. It is sometimes found in limestone, which in Ohio has been the chief oil-producing rock. These pools are most irregular and indefinite in shape, no two being alike. When broadly considered, they are often found to have a certain trend or definite direction across the territory in which they are found, involving in some cases a number of States. Accompanying oil and natural gas, and in the same rocks in which they are contained, large quantities of salt water are frequently found. It is not necessary here to go into further geological explanation of these facts.1

Natural Gas. As intimated in the preceding description of oil deposits, natural gas is only another product of the same substance which has produced both asphalt and petroleum, whatever that substance or source may have been. It simply represents the most volatile portions of such substances, the heavier having been converted, as is supposed, into bitumen, -which volatile portions have been driven off by the agencies above referred to. It is always found on top of the oil when immediately associated with it, but sometimes it is found isolated and far beneath the oil-producing strata in the vicinity. This is simply due to the fact that it was checked at this point in its upward course and collected there. Give it a chance, and it will always rise

1 By act of Congress, February 11, 1897, petroleum lands must be located as placer claims.

above the oil, being more volatile. While not a mineral in a mineralogical sense, it is so considered in law. For in a general legal sense any valuable inert or lifeless substance formed or deposited in its present position through natural agencies alone, and which is found either in or upon the soil of the earth or in the rocks beneath the soil, is a mineral. With a number of exceptions such as coal, graphite, limestone, infusorial earth, asphalt, petroleum and natural gas, phosphate rock, guano, nitrate of soda, amber (fossil resin), etc. these substances are of inorganic origin. The above definition is of course not a definition of the term as used in geology or mineralogy, but only as used in law and in commerce.

Sulphur. — This is a non-metallic mineral which has great commercial importance. Its principal occurrence in nature is either in the form of native sulphur or of a mineral known as iron pyrites; that is, a combination of sulphur and iron.

Native sulphur is found in large quantities in the neighborhood of extinct volcanoes or in craters of the volcanoes themselves, such as in the crater of Popocatepetl, etc. There are many deposits of it in the Andes, and in Mexico and in Sicily; but. it is also found in this country, as, for example, in Nevada, Utah, Yellowstone Park, and elsewhere, but always in very irregular superficial deposits. It is nearly always impure, that is, admixed with extraneous matter.

Iron pyrites, however, is a very different substance, and is a glistening yellowish mineral, which has been formed in the great majority of cases from the contemporaneous deposition and union of sulphur and iron solutions in presumably ascending hot alkaline waters or possibly vapors. This has been deposited in vast quantities in rifts or breaks in the rocky crust, and in other places in it suitable for the deposition of such mineral solutions. It is very often found in pockets or seams in limestones near eruptive rocks, or at the contact between these eruptive. rocks and the limestone, or some other rock, through which the eruptive rock when in a molten condition came up. Pyrites is mined in great quantities in Spain, Portugal, Newfoundland, and in the United States, but, for matter of that, all over the world, principally, however, for the other metals which may be associ ated with it, such as gold, silver, copper, nickel, etc., and which will be considered hereafter. It is a most important mineral,

and of very common occurrence in nature. For these reasons it will be referred to again under its proper classification as one of the metallic minerals. It is referred to at this time only because large quantities of sulphuric acid are manufactured from it.

Phosphate Rock. This is a very peculiar mineral, which is found in large quantities along the Atlantic border of the United States. Its chief use is in the manufacture of fertilizers. A mineral known as apatite, and which is largely composed of phosphate of lime, was formerly extensively mined in Canada, but owing to the discoveries in Florida of large deposits of so-called "high grade" phosphate rock it has ceased to be mined on a large scale.

The common variety of phosphate rock occurs in irregular superficial beds or as water-worn fragments or pebbles, the latter having very probably become detached from these irregular deposits, and sometimes carried great distances from their original source, by the action of the sea or rivers. Along with these phosphatic nodules or fragments there are found great numbers of fossil bones of many species, fossil teeth, etc., which have often been enriched by phosphate of lime, so that they now contain much more of this substance than originally.

as, for example, guano and These deposits, whatever

The theory which probably contains most truth with regard to the origin of these deposits is that they are due to immense ancient deposits of guano, or other remains or accumulations, derived from various forms of animal life, and which contained large quantities of phosphate of lime; the bones of animals are known to do. may have been their exact nature, are known to have been of great magnitude in Tertiary times, owing to the very great abundance of animal and especially of bird life, the latter favoring the theory of guano as the chief factor in producing the present material. According to this theory, when guano accumulated on a coral reef or on an exposed portion of a bed of limestone, the slow action of rain water falling upon it, or other phosphatic material, caused some of the soluble phosphates to be carried down and to be redeposited in the limestone or marl beneath. That is to say, such slightly acidulated water would readily take into solution the carbonate of lime, forming by far the greater part of the limestone, and leave behind its previous

load of phosphate of lime. In this way the process of substitution, or what is known as pseudomorphism or replacement, has taken place. Original fossil shells (carbonate of lime) are often met with which have been accurately replaced by phosphate of lime, so that they now contain a large percentage of the latter. This can be proved to have taken place in a great many instances, and it is doubtless as good a solution of the problem of the origin of these deposits as any which has yet been offered.

It is readily seen that these deposits are apt to be very superficial, unless covered by later sediments, and very irregular in shape. Most of them which have been worked, as in Florida, are of comparatively recent origin in a geological sense (Tertiary). Deposits of somewhat similar material have, however, been recently found in Devonian strata in Tennessee.

That great quantities of pebbles of phosphate rock are found, as, for example, in the southern portion of Florida, is owing to the fact that they are very insoluble; and when once a fragment of this substance has been detached from its original source, it could be carried many miles by ocean currents or by rivers, but would lose little or nothing except by attrition, simply becoming waterworn like any other pebble which is with difficulty soluble, like those of quartz, which are often found with the phosphate pebbles. These phosphate pebbles have been distributed over considerable areas, and subsequently collected in the rivers which traverse these areas, having obeyed the laws which govern the distribution of any other pebbles. In fact, the author sees no reason why they should be regarded as differing materially from any other pebble in their mode of origin, except as above stated. It is possible that the very irregular shape of some of the so-called "nodules," such as those which are found in South Carolina, for example, can be explained by the irregularity of the superficial replacement of the original limestone rock or perhaps marl. When small fragments were subsequently detached from such a deposit, the portions of such a fragment which contained a large quantity of phosphate of lime would remain, while the other portions, containing chiefly carbonate of lime, would be dissolved away. On the other hand, they sometimes show a distinct concretionary structure, when, of course, their origin must have been in the main like that of other concretions, - merely a segregation of the minute particles of lime phosphate, originally

diffused throughout portions of certain strata, until an irregular concretionary nodule was formed.

Clay Deposits. As will hereafter be seen, aluminum and alum are not extracted from the kinds of clay which are commonly met with, since they are not commercially suitable for the purpose, but, as is well known, many clay deposits, which would not be suitable for the manufacture of aluminum or of alum, are extensively mined and are used for other purposes, such as making brick, cement, pottery, etc. These beds of clay are often due to the superficial disintegration of the underlying rocks, when they are regarded simply as soil. Very frequently, however, they form distinctly stratified beds, as, for example, in the coal measures, where they are found immediately associated with and very often underlying the coal seams. These deposits are known by the name of fire clay, since the material is used for making fire brick. Very pure deposits are used for making pottery, and especially the unctuous material which is known as kaolin, which is simply a very pure form of clay, largely derived, it is supposed, from the disintegration of the mineral feldspar.

No matter to what such deposits of clay may owe their commercial value, it is clearly seen that they must necessarily fall within the legal classification of stratified deposits, and within the operation of the law which is applicable to such deposits. In the case of clay deposits or clay seams accompanying coal seams, they present no important points of difference in their mode of occurrence and stratified character from the latter, and necessarily the same legal reasoning must be applied to them, except so far as modified by statute.

Salt. Salt, or chloride of sodium, is a mineral-partly metallic in its nature, but not popularly so considered - which is very extensively mined in different parts of the world, and in some cases it is found in a very pure condition. It is always found occupying distinctly stratified beds, the exact origin of which is in some cases rather obscure, but it is sufficient to say that it has certainly been derived from the sea or salt lakes. That is to say, the deposits of rock salt probably originated on the sea bottom, or rather at the bottom of an enclosed lagoon which was filled with sea water at the spring tides or at other seasons, evaporation afterward taking place, leaving the salt behind. In many cases,