[Ill.u.s.tration 68 (Intersections of Veins): A, C--_Vena dilatata_ crossing a _vena profunda_. B--_Vena profunda_. D, E--_Vena dilatata_ which junctions with a _vena profunda_. F--_Vena profunda_. G--_Vena dilatata_. H, I--Its divided parts. K--_Vena profunda_ which divides the _vena dilatata_.]

But enough of _venae profundae_, their junctions and divisions. Now we come to _venae dilatatae_. A _vena dilatata_ may either cross a _vena profunda_, or join with it, or it may be cut by a _vena profunda_, and be divided into parts.

[Ill.u.s.tration 69a (Veins in mountain): A--The "beginning" (_origo_).

B--The "end" (_finis_). C--The "head" (_caput_). D--The "tail"

(_cauda_).]

Finally, a _vena profunda_ has a "beginning" (_origo_), an "end"

(_finis_), a "head" (_caput_), and a "tail" (_cauda_). That part whence it takes its rise is said to be its "beginning," that in which it terminates the "end." Its "head"[5] is that part which emerges into daylight; its "tail" that part which is hidden in the earth. But miners have no need to seek the "beginning" of veins, as formerly the kings of Egypt sought for the source of the Nile, but it is enough for them to discover some other part of the vein and to recognise its direction, for seldom can either the "beginning" or the "end" be found. The direction in which the head of the vein comes into the light, or the direction toward which the tail extends, is indicated by its footwall and hangingwall. The latter is said to hang, and the former to lie. The vein rests on the footwall, and the hangingwall overhangs it; thus, when we descend a shaft, the part to which we turn the face is the footwall and seat of the vein, that to which we turn the back is the hangingwall.

Also in another way, the head accords with the footwall and the tail with the hangingwall, for if the footwall is toward the south, the vein extends its head into the light toward the south; and the hangingwall, because it is always opposite to the footwall, is then toward the north.

Consequently the vein extends its tail toward the north if it is an inclined _vena profunda_. Similarly, we can determine with regard to east and west and the subordinate and their intermediate directions. A _vena profunda_ which descends into the earth may be either vertical, inclined, or crooked; the footwall of an inclined vein is easily distinguished from the hangingwall, but it is not so with a vertical vein; and again, the footwall of a crooked vein is inverted and changed into the hangingwall, and contrariwise the hangingwall is twisted into the footwall, but very many of these crooked veins may be turned back to vertical or inclined ones.

[Ill.u.s.tration 69b (Veins in mountain): A--The "beginning." B--The "end."

C, D--The "sides."]

A _vena dilatata_ has only a "beginning" and an "end," and in the place of the "head" and "tail" it has two sides.

[Ill.u.s.tration 70 (Veins in mountain): A--The "beginning." B--The "end."

C--The "head." D--The "tail." E--Transverse vein.]

A _vena c.u.mulata_ has a "beginning," an "end," a "head," and a "tail,"

just as a _vena profunda_. Moreover, a _vena c.u.mulata_, and likewise a _vena dilatata_, are often cut through by a transverse _vena profunda_.

[Ill.u.s.tration 71a (Fibra dilatata): A, B--Veins. C--Transverse stringer. D--Oblique stringer. E--a.s.sociated stringer. F--_Fibra dilatata_.]

Stringers (_fibrae_)[6], which are little veins, are cla.s.sified into _fibrae transversae_, _fibrae obliquae_ which cut the vein obliquely, _fibrae sociae_, _fibrae dilatatae_, and _fibrae inc.u.mbentes_. The _fibra transversa_ crosses the vein; the _fibra obliqua_ crosses the vein obliquely; the _fibra socia_ joins with the vein itself; the _fibra dilatata_, like the _vena dilatata_, penetrates through it; but the _fibra dilatata_, as well as the _fibra profunda_, is usually found a.s.sociated with a vein.

[Ill.u.s.tration 71b (Fibra inc.u.mbens): A--Vein. B--_Fibra inc.u.mbens_ from the surface of the hangingwall. C--Same from the footwall.]

The _fibra inc.u.mbens_ does not descend as deeply into the earth as the other stringers, but lies on the vein, as it were, from the surface to the hangingwall or footwall, from which it is named _Subdialis_.[7]

In truth, as to direction, junctions, and divisions, the stringers are not different from the veins.

[Ill.u.s.tration 72 (Seams in the Rocks): A--Seams which proceed from the east. B--The inverse.]

Lastly, the seams, which are the very finest stringers (_fibrae_), divide the rock, and occur sometimes frequently, sometimes rarely. From whatever direction the vein comes, its seams always turn their heads toward the light in the same direction. But, while the seams usually run from one point of the compa.s.s to another immediately opposite it, as for instance, from east to west, if hard stringers divert them, it may happen that these very seams, which before were running from east to west, then contrariwise proceed from west to east, and the direction of the rocks is thus inverted. In such a case, the direction of the veins is judged, not by the direction of the seams which occur rarely, but by those which constantly recur.

[Ill.u.s.tration 73 (Veins in mountain): A--Solid vein. B--Solid stringer.

C--Cavernous vein. D--Cavernous stringer. E--Barren vein. F--Barren stringer.]

Both veins or stringers may be solid or drusy, or barren of minerals, or pervious to water. Solid veins contain no water and very little air. The drusy veins rarely contain water; they often contain air. Those which are barren of minerals often carry water. Solid veins and stringers consist sometimes of hard materials, sometimes of soft, and sometimes of a kind of medium between the two.

But to return to veins. A great number of miners consider[8] that the best veins in depth are those which run from the VI or VII direction of the east to the VI or VII direction of the west, through a mountain slope which inclines to the north; and whose hangingwalls are in the south, and whose footwalls are in the north, and which have their heads rising to the north, as explained before, always like the footwall, and finally, whose rock seams turn their heads to the east. And the veins which are the next best are those which, on the contrary, extend from the VI or VII direction of the west to the VI or VII direction of the east, through the slope of a mountain which similarly inclines to the north, whose hangingwalls are also in the south, whose footwalls are in the north, and whose heads rise toward the north; and lastly, whose rock seams raise their heads toward the west. In the third place, they recommend those veins which extend from XII north to XII south, through the slope of a mountain which faces east; whose hangingwalls are in the west, whose footwalls are in the east; whose heads rise toward the east; and whose rock seams raise their heads toward the north. Therefore they devote all their energies to those veins, and give very little or nothing to those whose heads, or the heads of whose rock seams rise toward the south or west. For although they say these veins sometimes show bright specks of pure metal adhering to the stones, or they come upon lumps of metal, yet these are so few and far between that despite them it is not worth the trouble to excavate such veins; and miners who persevere in digging in the hope of coming upon a quant.i.ty of metal, always lose their time and trouble. And they say that from veins of this kind, since the sun's rays draw out the metallic material, very little metal is gained. But in this matter the actual experience of the miners who thus judge of the veins does not always agree with their opinions, nor is their reasoning sound; since indeed the veins which run from east to west through the slope of a mountain which inclines to the south, whose heads rise likewise to the south, are not less charged with metals, than those to which miners are wont to accord the first place in productiveness; as in recent years has been proved by the St. Lorentz vein at Abertham, which our countrymen call Gottsgaab, for they have dug out of it a large quant.i.ty of pure silver; and lately a vein in Annaberg, called by the name of Himmelsch hoz[9], has made it plain by the production of much silver that veins which extend from the north to the south, with their heads rising toward the west, are no less rich in metals than those whose heads rise toward the east.

It may be denied that the heat of the sun draws the metallic material out of these veins; for though it draws up vapours from the surface of the ground, the rays of the sun do not penetrate right down to the depths; because the air of a tunnel which is covered and enveloped by solid earth to the depth of only two fathoms is cold in summer, for the intermediate earth holds in check the force of the sun. Having observed this fact, the inhabitants and dwellers of very hot regions lie down by day in caves which protect them from the excessive ardour of the sun.

Therefore it is unlikely that the sun draws out from within the earth the metallic bodies. Indeed, it cannot even dry the moisture of many places abounding in veins, because they are protected and shaded by the trees. Furthermore, certain miners, out of all the different kinds of metallic veins, choose those which I have described, and others, on the contrary, reject copper mines which are of this sort, so that there seems to be no reason in this. For what can be the reason if the sun draws no copper from copper veins, that it draws silver from silver veins, and gold from gold veins?

Moreover, some miners, of whose number was Calbus[10], distinguish between the gold-bearing rivers and streams. A river, they say, or a stream, is most productive of fine and coa.r.s.e grains of gold when it comes from the east and flows to the west, and when it washes against the foot of mountains which are situated in the north, and when it has a level plain toward the south or west. In the second place, they esteem a river or a stream which flows in the opposite course from the west toward the east, and which has the mountains to the north and the level plain to the south. In the third place, they esteem the river or the stream which flows from the north to the south and washes the base of the mountains which are situated in the east. But they say that the river or stream is least productive of gold which flows in a contrary direction from the south to the north, and washes the base of mountains which are situated in the west. Lastly, of the streams or rivers which flow from the rising sun toward the setting sun, or which flow from the northern parts to the southern parts, they favour those which approach the nearest to the lauded ones, and say they are more productive of gold, and the further they depart from them the less productive they are. Such are the opinions held about rivers and streams. Now, since gold is not generated in the rivers and streams, as we have maintained against Albertus[11] in the book ent.i.tled "_De Subterraneorum Ortu et Causis_," Book V, but is torn away from the veins and stringers and settled in the sands of torrents and water-courses, in whatever direction the rivers or streams flow, therefore it is reasonable to expect to find gold therein; which is not opposed by experience.

Nevertheless, we do not deny that gold is generated in veins and stringers which lie under the beds of rivers or streams, as in other places.

END OF BOOK III.

FOOTNOTES:

[1] Modern nomenclature in the description of ore-deposits is so impregnated with modern views of their origin, that we have considered it desirable in many instances to adopt the Latin terms used by the author, for we believe this method will allow the reader greater freedom of judgment as to the author's views. The Latin names retained are usually expressive even to the non-Latin student. In a general way, a _vena profunda_ is a fissure vein, a _vena dilatata_ is a bedded deposit, and a _vena c.u.mulata_ an impregnation, or a replacement or a _stockwerk_. The _ca.n.a.les_, as will appear from the following footnote, were ore channels. "The seams of the rocks" (_commissurae saxorum_) are very puzzling. The author states, as appears in the following note, that they are of two kinds,--contemporaneous with the formation of the rocks, and also of the nature of veinlets. However, as to their supposed relation to the strike of veins, we can offer no explanation. There are pa.s.sages in this chapter where if the word "ore-shoot" were introduced for "seams in the rocks" the text would be intelligible. That is, it is possible to conceive the view that the determination of whether an east-west vein ran east or ran west was dependent on the dip of the ore-shoot along the strike. This view, however, is utterly impossible to reconcile with the description and ill.u.s.tration of _commissurae saxorum_ given on page 54, where they are defined as the finest stringers. The following pa.s.sage from the _Nutzliche Bergbuchlin_ (see Appendix), reads very much as though the dip of ore-shoots was understood at this time in relation to the direction of veins. "Every vein (_gang_) has two (outcrops) _ausgehen_, one of the _ausgehen_ is toward daylight along the whole length of the vein, which is called the _ausgehen_ of the whole vein. The other _ausgehen_ is contrary to or toward the strike (_streichen_) of the vein, according to its rock (_gestein_), that is called the _gesteins ausgehen_; for instance, every vein that has its strike from east to west has its _gesteins ausgehen_ to the east, and _vice-versa_."

Agricola's cla.s.sification of ore-deposits, after the general distinction between alluvial and _in situ_ deposits, is based entirely upon form, as will be seen in the quotation below relating to the origin of _ca.n.a.les_.

The German equivalents in the Glossary are as follows:--

Fissure vein (_vena profunda_) _Gang._ Bedded deposit (_vena dilatata_) _Schwebender gang oder fletze._ Stockwerk or impregnation (_vena c.u.mulata_) _Geschute oder stock._ Stringer (_fibra_) _Klufft._ Seams or joints (_commissurae saxorum_) _Absetzen des gesteins._

It is interesting to note that in _De Natura Fossilium_ he describes coal and salt, and later in _De Re Metallica_ he describes the Mannsfeld copper schists, as all being _venae dilatatae_. This nomenclature and cla.s.sification is not original with Agricola. Pliny (x.x.xIII, 21) uses the term _vena_ with no explanations, and while Agricola coined the Latin terms for various kinds of veins, they are his transliteration of German terms already in use. The _Nutzliche Bergbuchlin_ gives this same cla.s.sification.

HISTORICAL NOTE ON THE THEORY OF ORE DEPOSITS. Prior to Agricola there were three schools of explanation of the phenomena of ore deposits, the orthodox followers of the Genesis, the Greek Philosophers, and the Alchemists. The geology of the Genesis--the contemporaneous formation of everything--needs no comment other than that for anyone to have proposed an alternative to the dogma of the orthodox during the Middle Ages, required much independence of mind. Of the Greek views--which are meagre enough--that of the Peripatetics greatly dominated thought on natural phenomena down to the 17th century. Aristotle's views may be summarized: The elements are earth, water, air, and fire; they are trans.m.u.table and never found pure, and are endowed with certain fundamental properties which acted as an "efficient" force upon the material cause--the elements. These properties were dryness and dampness and heat and cold, the latter being active, the former pa.s.sive. Further, the elements were possessed of weight and lightness, for instance earth was absolutely heavy, fire absolutely light. The active and pa.s.sive properties existed in binary combinations, one of which is characteristic, _i.e._, "earth"

is cold and dry, water damp and cold, fire hot and dry, air hot and wet; trans.m.u.tation took place, for instance, by removing the cold from water, when air resulted (really steam), and by removing the dampness from water, when "earth" resulted (really any dissolved substance). The trans.m.u.tation of the elements in the earth (meaning the globe) produces two "exhalations," the one fiery (probably meaning gases), the other damp (probably meaning steam). The former produces stones, the latter the metals. Theophrastus (On Stones, I to VII.) elaborates the views of Aristotle on the origin of stones, metals, etc.: "Of things formed in the earth some have their origin from water, others from earth. Water is the basis of metals, silver, gold, and the rest; 'earth' of stones, as well the more precious as the common.... All these are formed by solidification of matter pure and equal in its const.i.tuent parts, which has been brought together in that state by mere afflux or by means of some kind of percolation, or separated.... The solidification is in some of these substances due to heat and in others to cold." (Based on Hill's Trans., pp. 3-11). That is, the metals inasmuch as they become liquid when heated must be in a large part water, and, like water, they solidify with cold. Therefore, the "metals are cold and damp." Stones, on the other hand, solidify with heat and do not liquefy, therefore, they are "dry and hot" and partake largely of "earth." This "earth" was something indefinite, but purer and more pristine than common clay. In discussing the ancient beliefs with regard to the origin of deposits, we must not overlook the import of the use of the word "vein" (_vena_) by various ancient authors including Pliny (x.x.xIII, 21), although he offers no explanation of the term.

During the Middle Ages there arose the horde of Alchemists and Astrologers, a review of the development of whose muddled views is but barren reading. In the main they held more or less to the Peripatetic view, with additions of their own. Geber (13th (?) century, see Appendix B) propounded the conception that all metals were composed of varying proportions of "spiritual" sulphur and quicksilver, and to these Albertus Magnus added salt. The Astrologers contributed the idea that the immediate cause of the metals were the various planets. The only work devoted to description of ore-deposits prior to Agricola was the _Bergbuchlin_ (about 1520, see Appendix B), and this little book exhibits the absolute apogee of muddled thought derived from the Peripatetics, the Alchemists, and the Astrologers. We believe it is of interest to reproduce the following statement, if for no other reason than to indicate the great advance in thought shown by Agricola.

"The first chapter or first part; on the common origin of ore, whether silver, gold, tin, copper, iron, or lead ore, in which they all appear together, and are called by the common name of metallic ore. It must be noticed that for the washing or smelting of metallic ore, there must be the one who works and the thing that is worked upon, or the material upon which the work is expended. The general worker (efficient force) on the ore and on all things that are born, is the heavens, its movement, its light and influences, as the philosophers say. The influence of the heavens is multiplied by the movement of the firmaments and the movements of the seven planets. Therefore, every metallic ore receives a special influence from its own particular planet, due to the properties of the planet and of the ore, also due to properties of heat, cold, dampness, and dryness. Thus gold is of the Sun or its influence, silver of the Moon, tin of Jupiter, copper of Venus, iron of Mars, lead of Saturn, and quicksilver of Mercury. Therefore, metals are often called by these names by hermits and other philosophers. Thus gold is called the Sun, in Latin _Sol_, silver is called the Moon, in Latin _Luna_, as is clearly stated in the special chapters on each metal. Thus briefly have we spoken of the 'common worker' of metal and ore. But the thing worked upon, or the common material of all metals, according to the opinion of the learned, is sulphur and quicksilver, which through the movement and influence of the heavens must have become united and hardened into one metallic body or one ore. Certain others hold that through the movement and the influence of the heavens, vapours or _braden_, called mineral exhalations, are drawn up from the depths of the earth, from sulphur and quicksilver, and the rising fumes pa.s.s into the veins and stringers and are united through the effect of the planets and made into ore. Certain others hold that metal is not formed from quicksilver, because in many places metallic ore is found and no quicksilver. But instead of quicksilver they maintain a damp and cold and slimy material is set up on all sulphur which is drawn out from the earth, like your perspiration, and from that mixed with sulphur all metals are formed. Now each of these opinions is correct according to a good understanding and right interpretation; the ore or metal is formed from the fattiness of the earth as the material of the first degree (primary element), also the vapours or _braden_ on the one part and the materials on the other part, both of which are called quicksilver.

Likewise in the mingling or union of the quicksilver and the sulphur in the ore, the sulphur is counted the male and quicksilver the female, as in the bearing or conception of a child. Also the sulphur is a special worker in ore or metal.

"The second chapter or part deals with the general capacity of the mountain. Although the influence of the heavens and the fitness of the material are necessary to the formation of ore or metal, yet these are not enough thereto. But there must be adaptability of the natural vessel in which the ore is formed, such are the veins, namely _steinendegange_, _flachgange_, _schargange_, _creutzgange_, or as these may be termed in provincial names. Also the mineral force must have easy access to the natural vessel such as through the _kluffte_ (stringers), namely _hengkluft_, _querklufte_, _flachekluffte_, _creutzklufft_, and other occasional _flotzwerk_, according to their various local names. Also there must be a suitable place in the mountain which the veins and stringers can traverse."

AGRICOLA'S VIEWS ON THE ORIGIN OF ORE DEPOSITS. Agricola rejected absolutely the Biblical view which, he says, was the opinion of the vulgar; further, he repudiates the alchemistic and astrological view with great vigour. There can be no doubt, however, that he was greatly influenced by the Peripatetic philosophy. He accepted absolutely the four elements--earth, fire, water, and air, and their "binary"

properties, and the theory that every substance had a material cause operated upon by an efficient force. Beyond this he did not go, and a large portion of _De Ortu et Causis_ is devoted to disproof of the origin of metals and stones from the Peripatetic "exhalations."

No one should conclude that Agricola's theories are set out with the clarity of Darwin or Lyell. However, the matter is of such importance in the history of the theory of ore-deposits, and has been either so ignored or so coloured by the preconceptions of narrators, that we consider it justifiable to devote the s.p.a.ce necessary to a reproduction of his own statements in _De Ortu et Causis_ and other works. Before doing so we believe it will be of service to readers to summarize these views, and in giving quotations from the Author's other works, to group them under special headings, following the outline of his theory given below. His theory was:--

(1) Openings in the earth (_ca.n.a.les_) were formed by the erosion of subterranean waters.

(2) These ground waters were due (_a_) to the infiltration of the surface waters, rain, river, and sea water; (_b_) to the condensation of steam (_halitus_) arising from the penetration of the surface waters to greater depths,--the production of this _halitus_ being due to subterranean heat, which in his view was in turn due in the main to burning bitumen (a comprehensive genera which embraced coal).

(3) The filling of these _ca.n.a.les_ is composed of "earth," "solidified juices," "stone," metals, and "compounds," all deposited from water and "juices" circulating in the _ca.n.a.les_. (See also note 4, page 1).

"Earth" comprises clay, mud, ochre, marl, and "peculiar earths"

generally. The origin of these "earths" was from rocks, due to erosion, transportation, and deposition by water. "Solidified juices" (_succi concreti_) comprised salt, soda, vitriol, bitumen, etc., being generally those substances which he conceived were soluble in and deposited from water. "Stones" comprised precious, semi-precious, and unusual stones, such as quartz, fluor-spar, etc., as distinguished from country rock; the origin of these he attributed in minor proportion to transportation of fragments of rock, but in the main to deposits from ordinary mineral juice and from "stone juice" (_succus lapidescens_). Metals comprised the seven traditional metals; the "compounds" comprised the metallic minerals; and both were due to deposition from juices, the compounds being due to a mixture of juices. The "juices" play the most important part in Agricola's theory. Each substance had its own particular juice, and in his theory every substance had a material and an efficient cause, the first being the juice, the second being heat or cold. Owing to the latter the juices fell into two categories--those solidified by heat (_i.e._, by evaporation, such as salt), and those solidified by cold, (_i.e._, because metals melt and flow by heat, therefore their solidification was due to cold, and the juice underwent similar treatment). As to the origin of these juices, some were generated by the solution of their own particular substance, but in the main their origin was due to the combination of "dry things," such as "earth," with water, the mixture being heated, and the resultant metals depended upon the proportions of "earth" and water. In some cases we have been inclined to translate _succus_ (juice) as "solution," but in other cases it embraced substances to which this would not apply, and we feared implying in the text a chemical understanding not warranted prior to the atomic theory.

In order to distinguish between earths, (clays, etc.,) the Peripatetic "earth" (a pure element) and the earth (the globe) we have given the two former in quotation marks. There is no doubt some confusion between earth (clays, etc.) and the Peripatetic "earth," as the latter was a pure substance not found in its pristine form in nature; it is, however, difficult to distinguish between the two.

ORIGIN OF Ca.n.a.lES (_De Ortu_, p. 35). "I now come to the _ca.n.a.les_ in the earth. These are veins, veinlets, and what are called 'seams in the rocks.' These serve as vessels or receptacles for the material from which minerals (_res fossiles_) are formed. The term _vena_ is most frequently given to what is contained in the _ca.n.a.les_, but likewise the same name is applied to the _ca.n.a.les_ themselves. The term vein is borrowed from that used for animals, for just as their veins are distributed through all parts of the body, and just as by means of the veins blood is diffused from the liver throughout the whole body, so also the veins traverse the whole globe, and more particularly the mountainous districts; and water runs and flows through them. With regard to veinlets or stringers and 'seams in the rocks,' which are the thinnest stringers, the following is the mode of their arrangement.

Veins in the earth, just like the veins of an animal, have certain veinlets of their own, but in a contrary way. For the larger veins of animals pour blood into the veinlets, while in the earth the humours are usually poured from the veinlets into the larger veins, and rarely flow from the larger into the smaller ones. As for the seams in the rocks (_commissurae saxorum_) we consider that they are produced by two methods: by the first, which is peculiar to themselves, they are formed at the same time as the rocks, for the heat bakes the refractory material into stone and the non-refractory material similarly heated exhales its humours and is made into 'earth,' generally friable. The other method is common also to veins and veinlets, when water is collected into one place it softens the rock by its liquid nature, and by its weight and pressure breaks and divides it. Now, if the rock is hard, it makes seams in the rocks and veinlets, and if it is not too hard it makes veins. However, if the rocks are not hard, seams and veinlets are created as well as veins. If these do not carry a very large quant.i.ty of water, or if they are pressed by a great volume of it, they soon discharge themselves into the nearest veins. The following appears to be the reason why some veinlets or stringers and veins are _profundae_ and others _dilatatae_. The force of the water crushes and splits the brittle rocks; and when they are broken and split, it forces its way through them and pa.s.ses on, at one time in a downward direction, making small and large _venae profundae_, at another time in a lateral direction, in which way _venae dilatatae_ are formed. Now since in each cla.s.s there are found some which are straight, some inclined, and some crooked, it should be explained that the water makes the _vena profunda_ straight when it runs straight downward, inclined when it runs in an inclined direction; and that it makes a _vena dilatata_ straight when it runs horizontally to the right or left, and in a similar way inclined when it runs in a sloping direction. Stringers and large veins of the _profunda_ sort, extending for considerable lengths, become crooked from two causes. In one case when narrow veins are intersected by wide ones, then the latter bend or drag the former a little. In the other case, when the water runs against very hard rock, being unable to break through, it goes around the nearest way, and the stringers and veins are formed bent and crooked. This last is also the reason we sometimes see crooked small and large _venae dilatatae_, not unlike the gentle rise and fall of flowing water. Next, _venae profundae_ are wide, either because of abundant water or because the rock is fragile. On the other hand, they are narrow, either because but little water flows and trickles through them, or because the rock is very hard. The _venae dilatatae_, too, for the same reasons, are either thin or thick. There are other differences, too, in stringers and veins, which I will explain in my work _De Re Metallica_.... There is also a third kind of vein which, as it cannot be described as a wide _vena profunda_, nor as a thick _vena dilatata_, we will call a _vena c.u.mulata_. These are nothing else than places where some species of mineral is acc.u.mulated; sometimes exceeding in depth and also in length and breadth 600 feet; sometimes, or rather generally, not so deep nor so long, nor so wide. These are created when water has broken away the rock for such a length, breadth, and thickness, and has flung aside and ejected the stones and sand from the great cavern which is thus made; and afterward when the mouth is obstructed and closed up, the whole cavern is filled with material from which there is in time produced some one or more minerals. Now I have stated when discoursing on the origin of subterranean humours, that water erodes away substances inside the earth, just as it does those on the surface, and least of all does it shun minerals; for which reason we may daily see veinlets and veins sometimes filled with air and water, but void and empty of mining products, and sometimes full of these same materials. Even those which are empty of minerals become finally obstructed, and when the rock is broken through at some other point the water gushes out. It is certain that old springs are closed up in some way and new ones opened in others. In the same manner, but much more easily and quickly than in the solid rock, water produces stringers and veins in surface material, whether it be in plains, hills, or mountains.

Of this kind are the stringers in the banks of rivers which produce gold, and the veins which produce peculiar earth. So in this manner in the earth are made _ca.n.a.les_ which bear minerals."

ORIGIN OF GROUND WATERS. (_De Ortu_ p. 5). "... Besides rain there is another kind of water by which the interior of the earth is soaked, so that being heated it can continually give off _halitus_, from which arises a great and abundant force of waters." In description of the _modus operandi_ of _halitum_, he says (p. 6): "... _Halitus_ rises to the upper parts of the _ca.n.a.les_, where the congealing cold turns it into water, which by its gravity and weight again runs down to the lowest parts and increases the flow of water if there is any. If any finds its way through a _ca.n.a.les dilatata_ the same thing happens, but it is carried a long way from its place of origin. The first phase of distillation teaches us how this water is produced, for when that which is put into the ampulla is warmed it evaporates (_expirare_), and this _halitus_ rising into the operculum is converted by cold into water, which drips through the spout. In this way water is being continually created underground." (_De Ortu_, p. 7): "And so we know from all this that of the waters which are under the earth, some are collected from rain, some arise from _halitus_ (steam), some from river-water, some from sea-water; and we know that the _halitum_ is produced within the earth partly from rain-water, partly from river-water, and partly from sea-water." It would require too much s.p.a.ce to set out Agricola's views upon the origin of the subterranean heat which produced this steam. It is an involved theory embracing clashing winds, burning bitumen, coal, etc., and is fully set out in the latter part of Book II, _De Ortu et Causis_.

ORIGIN OF GANGUE MINERALS. It is necessary to bear in mind that Agricola divided minerals (_res fossiles_--"Things dug up," see note 4, p. 1) into "earths," "solidified juices," "stones," "metals," and "compounds;"

and, further, to bear in mind that in his conception of the origin of things generally, he was a disciple of the Peripatetic logic of a "material substance" and an "efficient force," as mentioned above.

As to the origin of "earths," he says (_De Ortu_, p. 38): "Pure and simple 'earth' originates in the _ca.n.a.les_ in the following way: rain water, which is absorbed by the surface of the earth, first of all penetrates and pa.s.ses into the inner parts of the earth and mixes with it; next, it is collected from all sides into stringers and veins, where it, and sometimes water of other origin, erodes the 'earth' away,--a great quant.i.ty of it if the stringers and veins are in 'earth,' a small quant.i.ty if they are in rock. The softer the rock is, the more the water wears away particles by its continual movement. To this cla.s.s of rock belongs limestone, from which we see chalk, clay, and marl, and other unctuous 'earths' made; also sandstone, from which are made those barren 'earths' which we may see in ravines and on bare rocks. For the rain softens limestone or sandstone and carries particles away with it, and the sediment collects together and forms mud, which afterward solidifies into some kind of 'earth.' In a similar way under the ground the power of water softens the rock and dissolves the coa.r.s.er fragments of stone.