into anthracite. The anthracites themselves vary greatly in their composition and in the amount of volatile matter which remains in the coal. As more and more of this volatile matter is driven off we find, as in the other grades, even the anthracite gradually becoming more and more graphitic in character, like the coal, of Rhode Island, for example, until we finally arrive at pure graphite. The latter is usually found only in the oldest known sedimentary rocks.

Of course coals vary greatly one from the other in the matter of purity. Some of them contain little or nothing outside of that contained by the original vegetable matter, to the decomposition of which they owe their origin. On the other hand, some are found containing great quantities of sand and mud, which were washed into or over the peat swamps forming, as is usually thought and has been pointed out, near the mouth of some broad river emptying into an arm of the sea. This sand or mud has of course remained in the coal ever since. Iron and sulphur are frequently found in coal, forming, when combined, iron pyrites, and affecting its value greatly. The lawyer, however, is concerned more with the geological or physical peculiarities of such a deposit; that is to say, its mode of occurrence, its general form, and its extent. As has already been stated, a single bed especially when the strata are horizontal or nearly so is often extensive over a very large area, many square miles in extent. It is found close to the surface or at very great depths below it, according to the present topographical conditions of the country, that is, according to the amount and extent of erosion, or according to the position of the strata in which it is included, or very often according to what is called the dip or inclination of the This can be readily understood by reference to the diagrams. In this connection the effect of erosion, which has carried away large areas of coal beds, along with portions of the strata which contain them, is also to be noted. As already stated, beds of coal vary in thickness from a few inches or a mere band to a number of feet, but the seams which are usually worked in this country vary from three feet or a little less to eleven or twelve feet. Sometimes, however, they greatly exceed this thickness. A coal bed does not always maintain its thickness, but is frequently found to be much thinner at some places than at others. In this respect, nevertheless, it furnishes a great exception to

same.

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most other mineral deposits, as it is much more regular and more nearly maintains its thickness than any other class of deposits.

It is to be noted in this connection that a deposit of coal is properly referred to as a coal bed or coal seam, and not a coal vein. As will be seen hereafter, a vein usually presupposes an original break or rift - often an old fault in the rocks, through which crack, mineralized waters have subsequently made their ascent. An accumulation of peaty material, however, being more or less a sedimentary deposit, is properly referred to as a bed, in the way we speak of a bed of sandstone, or bed of shale, or bed of limestone. Indeed we often have coaly (carbonaceous or bituminous) shales, or "black slate," as it is commonly called by the miners, containing, we will say, five per cent combustible matter and ninety-five per cent ash, which means simply that a little peaty or vegetable matter got mixed with the mud at the time the latter was deposited.

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Asphalt. This is a curious mineral, the origin of which is not at all well understood. It is supposed, however, that it is derived from certain kinds of organic matter in salt water, not fresh or brackish water, like coal, — whether vegetable or animal, or both, it makes little difference. It is a significant fact that it is always found in connection with sedimentary fossiliferous rocks, from Paleozoic up to Tertiary, and it is this which gives rise to the supposition that it has its origin in some kind of marine life, the structure of which may have been such as to leave no other evidence of its existence. It is a black tarry substance, with the peculiar odor of bitumen. Asphalt sometimes is found forming great pools or lakes, which in some cases have probably exuded from the inferior or adjoining rocks. An example of a deposit of this kind is the famous pitch lake on the island of Trinidad. More frequently it is found impregnating or saturating certain rocks, but only those of sedimentary origin; that is, either limestones, sandstones, or shales. In some cases it is found impregnating a portion of a coal bed, and the so-called cannel coal is supposed by some to owe its extremely bituminous nature to an admixture with the coal seams of the organic material from which asphalt has been produced.

In Kentucky, Indian Territory, Utah, and California there are quite thick strata which are in places heavily impregnated with

this asphalt or bitumen. In some of these areas, where there are crevices or cracks in the rock, these crevices are filled with this bituminous substance or asphalt (Utah and California). According to the amount of oxygenation which this substance has undergone in these cracks it has given rise to many different but kindred minerals, the principal among which are albertite (Nova Scotia), grahamite (West Virginia), gilsonite and ozokerite (Utah).

Asphalt itself seems to be the residue of the distillation of the more volatile oils, or it may be that these oils have by some metamorphic agencies (heat, pressure, etc.) been converted into it. It is very variable in composition, and is usually mixed with extraneous material. With the exception of the lake of Trinidad mentioned, and some deposits in Venezuela, - where it is found in a very pure condition relatively speaking, and is dipped up, put into barrels, and shipped away in the crude state,it is usually mined in connection with the rock which contains it, and it is used for paving material in this condition. This crude material, however, is usually refined. Very rarely it is found forming what seems to be a coal bed, so absolutely stratified is it, and so comparatively free from impurities. This occurrence is, however, rare, and when seen, such a deposit is usually found to become, in a short distance, more and more admixed with the material forming the adjacent rocks.

With regard to its mode of occurrence, therefore, it is only necessary to remember that it is usually found impregnating, saturating, or admixed with the material which forms some sedimentary stratum, and is never found in eruptive rocks, in which respect it is like coal, though differing from it widely in others. In Kentucky, Indian Territory, Utah, and California these strata are sandstones, while the chief asphalt deposits in Europe are in limestone. The veins or crevices in which the kindred minerals (gilsonite, etc.) above mentioned are found in Utah, California, West Virginia, and Nova Scotia would probably be classed in a legal sense, as they would certainly be in a geological sense, as true fissure veins, although they do not contain any metallic minerals. As those upon government lands are principally found upon land which is now included in Indian Reservations, the ques tion as to their legal classification has not yet arisen; but upon the lines of reasoning followed by our courts with regard to recog

nizing the geological or physical differences between the various classes of valuable mineral deposits, and basing important legal distinctions upon these, rather than upon the chemical or mineralogical differences of the substances contained in the deposit, it is suggested that since these minerals are found filling true fissures, the deposit would properly be located as a "lode," and what is known as the law of the apex would rule.1

Petroleum.Petroleum, or mineral oil, is as much a mineral in a legal sense as though it were of a metallic nature. Its origin is quite certainly more or less similar to that of asphalt, and probably it and its kindred substances represent the more volatile oils, which either have been distilled off of the original deposit of bituminous material contained in shales, limestones, and sandstones, leaving the heavier material (asphaltum) behind, or which, when subjected to metamorphic influences, were converted into it. It is often found in or above rocks which contain the deposits of asphalt; that is to say, the two belong to the same series of strata, or approximately so. In fact, it is supposed by some that many of the deposits of asphaltic sandstone and limestone, or other rocks with which this substance is admixed, simply represent what is left of the original material, whatever it may have been, after vast quantities of petroleum and the more volatile oils and gases have escaped. Others contend that these asphalt deposits simply represent in themselves old oil pools converted into asphalt by being exposed to the atmosphere or other oxygenating influences.

If the former theory is the correct one, as is probable, these asphaltic deposits, if they are now in the condition of asphalt, are

1 In the writer's opinion this view does not conflict with the opinion of Secretary Teller, 1 L. D. 561.

to be found perhaps several thousand feet below the present surface, that is, considerably below the present oil-bearing strata; and the more volatile substances (petroleum and natural gas), owing to the heat produced by the blanketing effect of the superimposed sediments, or for any other reason, have escaped from this, their original source of bituminous material, and ascended until their further progress was checked by some impervious stratum. This is usually some bed of clay or slate (shale), or what has produced the same effect, the so-called "shell" of closely cemented grit or other dense impervious material. In this way the oil and the gas which accompanies it have usually collected, and often in great quantities, in the open-textured or porous sandstones and grits beneath this stratum, but are not found in the other rocks of the series which are more dense. The latter are principally shales and fine-grained sandstones. It is, however, found in great quantities in limestone beds, but only where the surrounding conditions have made this a suitable repository. In this connection it should be remarked that oil, like water, is found only in rocks which are porous or contain fissures and cavities, great or small, i. e. sandstones or limestones. Conversely, the rocks which, like shales, are not water-bearing in a general sense are not oilbearing.

It must not be supposed that the oil generally occupies great or small subterranean cavities, although possibly it may rarely be found doing so, as in limestone. It usually occurs in nature as simply occupying the spaces or interstices or so-called pores between little pebbles and grains of sand in some rather opentextured but not necessarily incompact rock, or now and then is collected in the fissures and cavities of such rocks. Its source is quite certainly below the point at which it is at present found, because it will usually ascend and escape through any outlet it may find, owing to the elasticity of the accompanying gas. When there is a gentle roll or anticlinal fold or "saddle" in the strata, oil and gas are often found occupying, though very irregularly, positions in the crest of this fold underneath the impervious stratum. It does not seem to be found in large quantities in strongly folded strata, owing to the fact that the metamorphic agencies which caused the folding and tilting of the rocks have either converted the lighter oils into the more solid asphalt, or, as is more likely, the upturned and eroded strata have afforded these light