auc yet nee a onthe ee < Ne aan Ses eee ahd a pastas Rater Naraprt A RGEM Se ee a ics ndaent oli eteeal Ane ee se eS ad = > y a ee ~~ ? - pe ee < pela an it wi en athe PYRE alg hella tee ttn oT bs. Pe Mn tine ete Sethe omen Dy ale Be 0h Pag Peele th tlt aire Dele ian hg Atm Fat oegetin ep rete on Be ~S Be Patines reel ee a oan Basle Verein Bea ef apes SoA gn A at aay 8 oe ete at lt a Bo om rial esi fon hie PLateag Molin iy agit he Map gdm Mud grea pn Neatly gt hs ering yea ete ete: . Start : Spies Nal = len hn pK Ps Tiedt aiid tede ay rep aare e ee Aaterrnes ont ar non ee hn ta 2 ge tae am ing he PE, Be wpe: met actin tne Tears ale Pe eM RO Oe eae Pee ne tn eadlem ~ aa nee a a Ne HN ee a $ —— ere een Ah See Ny S-tty oe Pare els Dade IN r aA ee pee ee Sta ee ces oe et tena My ® fl | 2 Wf a fat Rea bat Wee One —— OLONJay> SS MALY tN en atta Prag atts " “A ¢ Di Wines es ae ates ie niet v i ee oe 7 be ae * on 7 ‘ va ve AN AA bats ; ; ; iw Al Nike? if ee pa Sey ey « iG ‘ : hak ¢ 4 OU. ¥ . iy al ire! ve a 7 ¢ » 7 « ra a st “So ip" ) \ ; me, » oan 3 es Ks BF ots artes i poe ( le SLRA ON THE CONNEXION OF GEOLOGY TERRESTRIAL MAGNETISM: SHOWING THE GENERAL POLARITY OF MATTER, THE MERIDIONAL STRUCTURE OF THE CRYSTALLINE ROCKS, THEIR TRANSITIONS, MOVEMENTS AND DISLOCATIONS, INCLUDING THE SEDIMENTARY ROCKS, THE LAWS REGULATING THE DISTRIBUTION OF METALLIFEROUS DEPOSITS, AND OTHER MAGNETIC PHENOMENA. BY EVAN HOPKINS, C.E., F.GS. “* Amid all the revolutions of the globe, the economy of Nature has been uniform, and her laws are the only things that have resisted the general movement. The rivers and the rocks, the seas and the continents, have been changed in all their parts ; but the laws which direct those changes, and the rules to which they are subject, have remained invariably the same.’’—Playfair. WITH TWENTY-FOUR PLATES. e LONDON: RICHARD AND JOHN EDWARD TAYLOR, RED LION COURT, FLEET STREET. 1844. PRINTED BY RICHARD AND JOHN E. TAYLOR, RED LION COURT, FLEET STREET. U PREFACE. ‘Tue principal object of this little work is to point out the general order and uniformity of rocks, and the mode in which minerals are disseminated and concentrated in them. There is no branch where there is so much capi- tal expended without any established principle to guide us aS mining—the opinion of a practical miner being often the only inducement to carry on a mine; and when two practical men differ, there is no data at pre- sent by which a third person can decide who is right. Both persons may be governed by the indications ob- served in their respective district, neither of which may be applicable to a mine in another locality. With the view of obtaining some well-founded prin- ciple to guide us in our subterranean works, the Author, during several years’ professional engagement in this pursuit, has paid very considerable attention to the sub- ject, both in America and Europe : this brief sketch is the result of his investigations. The principle here brought 1V ; PREFACE. forward has not been assumed to account for a particu- lar phenomenon, but has been established by the facts, and proved by several years’ experience, so that its ap- plication will enable a person to predict the general nature of the crystalline rocks, metalliferous deposits, and dislocations of any mining district. With regard to the other points which the above principle leads to, there is no doubt they will be opposed by theoretical persons ; however, this cannot interfere with the prac- tical operations of the mining engineer; he may safely trust to the laws of terrestrial physics, and leave time to prove which has the best foundation. In conclusion, the Author hopes that his humble endeavours, combined with the local knowledge of practical men, will lead to new discoveries, avoid so much ‘‘ guess-work ’’ and un- profitable undertakings, and thus tend to render this branch of our national wealth more certain and prospe- rous than it has hitherto been. February 1, 1844. CONTENTS. Introduction .... CHAPTER I. @n the Polarity of the Earth's Magnetism ................... CHAPTER II. The Identity of Magnetic and Galvanic Currents ............ CHAPTER III. On the Reduction of Metals by Electro-Magnetism or Galvanic POGRETCS HE ee eR ie cee? Ale ors er avech Meals CHAPTER IV. On Heat produced by the Magnetic or Galvanic Fluid........ CHAPTER V. Terrestrial Magnetism, or the Effects of the Positive and Nega- tive Poles of the Globe on all Substances within the limits of their actions.—Cleavage Planes, &c. .......... 0.0000 0eee CHAPTER VI. On the General Character of the Crystalline Rocks called “ Pri- many. -—ramite, Gneiss, Schist, &¢. 1... ke CHAPTER VII. On the Order of the Splits, Fractures and Dislocations in the Primary Rocks, including the Superincumbent Sedimentary Micisses:—=It eaves. SHES, Se@. cunt ie ae es ee ek ue ee CHAPTER VIII. Mineral Veins, their Mode of Filling, and the General Character of their Contents.—Roots and Branches of Mineral Veins.—The Influence of the Impermeable Splits on the Accumulation of Mi- nerals in the Transverse Fractures.—Recapitulation ........ 23 28 35 VI CONTENTS. CHAPTER IX. Pate Quicksilver Deposits, Saliferous Deposits, &c................. 58 CHAPTER X. Polarityot Barthquakes.... oreea wont ke oe en 64 CHAPTER XI. The Northward and Undulating Movement of the Earth’s Surface en masse, by the Constant Circulating Action of the Magnetic Currents sy cee cee OR see tei CHAPTER XII. The Northward Movement of the Surface proved by the Climate of the Land in the Northern Hemisphere getting colder ..... 72 CHAPTER: Xit. The Division of the Surface of the Globe into Zones of Deposition 80 CHAPTER XIV. On the General Nature of the Distribution of Heat over the Sur- face of the Globe, and the Zones of equal Temperature...... 92 CHAPTER XV. On the Positions, Undulations, Contortions and Fractures of the Sedimentary Rocks.—Faults, &c......... 0.606202 eee 101 CHAPTER XVI. General’ Observations... +2... To oe See ee eee 110 Universal: Magnetism: 2.2 2.6 so Se ys eee ee 112 CHAPTER XVIIL. On the General Application of Laws of Terrestrial Magnetism.. 124 DESCRIPTION OF THE PLATES. . An Illustration of the General Effects of Magnetism on an Artificial Globe. . The Nature of the Influence of Magnetic Globes on each other. . Magnetism of the Solar System. . The two Hemispheres, exhibiting the general Lamination of the Crystalline Rocks, and the Direction of the Magnetic Currents. . Ditto, North and South Poles. . Transition of the Granite into Gneiss and Schist in a North- erly Direction. . Meridional Direction of the Mexican Mines. Meridional Direction of the Mines of Cornwall. . The Meridional Lamination of the British Islands. . Heaves. . Veins of Fractures obliterated by a New Cleavage. . An Illustration of Right- and Left-hand ‘ Heaves.’ Isolated Masses of the Bounding Rocks in Veins of Fractures. . Different Angular Position of Veins. . An Illustration of the relative Position of the Bunches of Mineral in Veins. . Sections of the Primary and Sedimentary Rocks. . Influence of Splits on the Accumulation of Mineral in Veins of Fractures. . Silver Mine in New Grenada (Split Veins). . Gold Mine in New Grenada (Veins of Fractures). An Illustration of the Atmospherical Refraction, Tempera- ture, &c. . The Parallelism of similar Minerals in Veins of Fractures, showing the Meridional Action of the Metalliferous Currents through the Pores of the Rocks. . Veins enclosed in the Lamine of the Schistose Rocks. The Nature of Faults in Coal-beds. An Illustration of the Composition of Forces. sok cae Weipa te aa SA as a =, 4 — Ss | i 9 x hh Ae DAE lod é SE) hes fs ; y cy SA RT Ae te ade el a a A ghee Oot teen AN OUTLINE OF GEOLOGY, SHOWING ITS CONNEXION WITH THE LAWS OF TERRESTRIAL MAGNETISM. INTRODUCTION. ALTHOUGH geology has been brought, and now established as a distinct science, it must be admitted that the theories pro- mulgated to account for the observed phenomena are in a most crude state —contrary to analogy, and not only unsupported by, but in direct opposition to, the evidence afforded by the pheno- mena themselves. We search in vain for any useful fundamen- tal rules to guide us in subterraneous operations, even in a trea- tise professedly called practical, much less in those of a more theoretical character. Indeed the science may be considered at present as ‘ Fossil Geology ® combined with Comparative Ana- tomy,—principally confined to the examination of the relics of the past entombed in the sedimentary rocks, which branch, being somewhat more enchanting, has monopolized nearly the whole attention and interest of this more generally useful science. If we refer to the descriptions of the Primary rocks, we find them so imperfect and so inapplicable to their general structure, and mixed so much with hypothetical ideas, that those who derive all their knowledge from books must imagine these rocks as con- fused igneous masses void of all order. Those who are practi- cally acquainted with the subject have a very different opinion, and know that the crystalline rocks possess an harmonious sym- metrical structure. It is a very common remark in geological books, that great mistakes are committed in mining and other subterraneous works B 2 owing to the want of a better acquaintance with the geological nature of rocks; yet no definite rules have ever been suggested to avoid the repetition of such errors. It has been triumphantly appealed to, as one important generalization among others esta- blished by geology for the aid of miners, that the proximity of pyrogenous and sedimentary rocks, and the changes thus super- induced upon the latter regulate the enrichment and product- iveness of mineral veins. In this manner, it is said, that -cer- tainty and precision have been given to a knowledge which was before only vague and partial. It is not easy to comprehend the meaning, much less the application, of the above principle to mining, or any other works in rocks. There is scarcely a geological section furnished of the primary series in which the lamine of the crystalline slates are not confounded with the planes of the sedimentary strata; and also exhibiting veins with an overflow of melted matter, &c., showing volcanic effects, to explain phenomena with which they have no connexion. Every | hornblendic vein is now called ancient lava; and igneous or vol- canic rocks are terms of common occurrence. We shall en- deavour to show that there is no foundation for assuming such an igneous element, and that the crystalline rocks and the veins are formed by polar forces according to geometrical laws, as uniform as any other physical phenomena of the material world. This brief outline of the science is not brought forward with the view of showing the inconsistencies of the existing hypo- theses to explain the facts, nor to gratify idle curiosity by enter- ing into pure speculative questions, but to point out a general law, which is stmple and practically useful, consistent with the general law of terrestrial physics, and which has been suc- cessfully applied for several years in mining and other geological operations. Although the subject is confined here within narrow limits, and must necessarily be very imperfectly described, yet it is hoped that, by the aid of the accompanying illustrations, the general bearing of the magnetical theory will be comprehended, and found to rest on unquestionable data, without straining any facts, but simply following the legitimate consequences arising . from cause and effect, proved by direct examination and experi- ment. CHAPTER I. ON THE POLARITY OF THE EARTH’S MAGNETISM. Persons who have not paid attention to this interesting ques- tion, may consider this term as simply applied to magnetic needles, but we may observe that it is a property connected with al] matter, and that it has an important influence on the general economy of nature. It is well known that if a mag- netic bar be supported in such a manner as to have entire freedom of motion in a horizontal plane, it will, after a few oscil- lations, finally settle in a position directed more or less north and south. If disturbed from this situation and placed in any other direction, it will, as soon as it is again at liberty to move, resume its former position. The two ends are called its poles; the one which turns to the north being distinguished as the north and the other as the south pole; the tendency of the mag- net to assume the above described position is called its polarity. On this property is founded the mariner’s compass, which is of such essential use in navigation, and by the aid of which the mariner, however distant from land, amidst cloudy skies, or in the darkest nights, is enabled at all times to steer his course with certainty, and traverse in all directions the wide expanse of the ocean which separates the countries and continents of our globe. In exploring subterranean excavations, and, in a word, in all in- vestigations which have reference to the meridian, its aid is equally available. When we reflect on the great benefit mankind has derived from the polarity of magnetism alone, and which has so much contributed to advance the civilization of the human race, it must necessarily create a desire to learn something of its general character. It was considered for a long time that the only substance sus- ceptible of magnetism was iron and its oxides, but recent disco- veries have proved that there is no substance but which, under suitable circumstances, is capable of exhibiting unequivocal signs of the magnetic virtue, i.e. radial or lateral attraction, and the usual polar phenomena. The crystalline rocks, constituting the B 2 4 solid surface of the globe, are more or less magnetic, and cause great variations in the direction of the magnetic needle; nor is the needle ever free from this combined influence. It is well known, although not always taken into considera- tion, that the magnets were originally made out of a rock called a loadstone! a rock impregnated with iron in a state of oxide. All primary crystalline rocks containing iron and manganese will, with due delicacy, point north and south like the steel needles, 2. e. in the exact direction in which they are found in situ, when fresh cut from the place where they were formed. The above facts have been more or less proved by various ex- periments made in the equatorial regions. Indeed, these effects have been more or less observed in every part of the world,—in the Straits of Magellan, along the whole range of the Andes, in Mexico, North America, the Arctic Regions, in Scotland, and in various parts of the continents of Kurope and Asia. Not only is this influence of terrestrial mag- netism observed in the solid substances which constitute the sur- face, but the atmosphere has been proved to be equally affected by it. This last phenomenon was observed by me on various oc- casions whilst making magnetical experiments in South America; and the same has been observed by various persons in Europe, and more especially when the aurora borealis makes its appear- ance; and, to make use of the happy term applied by Humboldt, there appears to be “ magnetical storms,” probably arising from the equilibrium of the fluid bemg disturbed. They are very com- monly observed before and durimg earthquakes in equatorial America. The two hemispheres are represented in Plates IV. and V., on which will be observed the present average direction of the magnetic needles, according to Barlow’s ‘Magnetic Chart of Variations.” It will be seen that, notwithstanding the numerous local disturbances which the needles must be subject to, they preserve a remarkable degree of uniformity from pole to pole; and when we reflect on the delicate nature of our instruments, and consider how slight an action will cause a deviation from the line of equilibrium, we should, or ought to be, astonished that their general direction is so near the true meridian, rather than it should vary a little from it. i It must be borne in mind that the magnetic meridians in the Plates only represent the present, and that these directions are perpetually varying to either side of the true meridian, within an arc of about 15° at the equator, and about 60° near the polar circle. The direction of the magnetic needle in England about 250 years ago was 11° east of north, it is now about 25° west of north ; it is constantly undergoing a slow oscillation. The following Table shows the change which has taken place in London from the years 1576 to 1831 * :— Years. Variations. Years. Variations. 1576 | 1115 0 €Easterly.|| 1760 | 19 30 0 Vesterly. 1580 Li 7 Se | alae 1774 DF 20-0 1622 GZ, Or; 1778 Viph%) i ele Daa 1634 Be Bo 3 Oire i: 1790 IFT 39 ys Ono ks 1657 Wewtntt 1800 O43, Ors 1662 No Variation. 1806 Oa, gh Gils 1666 0 34 OWesterly.|| 1813 2A 20 VG acts: 1670 Ore u. . 13l5 | 27 27 18, 1672 223000) iy 1SIG > GTA GF vi;: 1700 GAG: 0.20), 1820. 24) i Hes, Peo 1G - OO. +), 1823 | 24 9 40 _,, 1740 | 1610 0 - 1831 ip ell | oa Lea Besides the progressive changes in the direction of theneedles, there are annual or periodical movements and daily oscillations constantly taking place in all parts where magnetic observations have been made. The dip of the needle, like the horizontal variation, has different values in different parts of the globe; on an average, being nothing or horizontal near the equator, and perpendicular to the horizon at the poles. Hence, if a magnetic needle were to be balanced at the equator, it would be found to decline from its horizon as we proceed from thence towards the poles; its average position forms a curve, called the ‘ Magnetic Curve,’ from pole to pole, as shown in Plate IV. On looking at the general direction of the magnetic curves and the magnetic meridians, we plainly observe that they tend * See Brewster’s Treatise on Magnetism. 6 to converge at the poles; notwithstanding their deflexions and undulations from various local disturbances, yet they preserve a remarkable degree of regularity. Numerous fruitless investiga- tions have been made with the view of ascertaining the position of the magnetic pole, as if that must be a mathematical point. Any person who has had some experience with the action of fluids, whether water, air, or electric, converging towards or di- verging from a central passage, must know that they cannot be forced into a mathematical point, there must be a limit to their compression or density ; nor can it be expected that every indi- vidual current should retain its exact radial course towards the focus, and much less when diverging from it. Hence, from analogy and observations, the narrowest limits that we can assign to the polar axis to which the magnetic currents converge and diverge are, perhaps, the areas bounded by the arctic and an- tarctic circles. By taking these extensive spaces for the magnetic poles, we shall be relieved from entering into the useless and endless in- quiries respecting late discoveries, and formulas which have been established or founded on them. The question is rendered simple, not requiring formule which profess great accuracy in points where the data of observation must be very uncertain. Although on an average the magnetic meridians, described in Plate [V., may be considered to approximate to the average di- rection at the present time, yet it must be kept in mind that-a great proportion of the lines have been assumed; however, they are sufficiently near for our present question. Numerous observations have been made in the equatorial regions, indicating both east and west variations in the same meridian of only a few leagues in extent; and numerous other experiments and observations may be quoted to prove that the direction of the needle does not necessarily point towards the centre of convergence of the individual current which moves it, but in the direction of the resultant, viz. the compound of the primary and local currents—the diagonal of the parallelo- gram of the two actions. The local disturbing force being a variable quantity subject to perpetual fluctuations, it follows as a consequence that the variations of the direction must be 7 uncertain, and therefore not within the power of any formule to know their periodical amount. In the above, our observations have been principally confined to the magnetic needle; but as it is proved that all matter is more or less affected by the magnetic fluid or current, and since we cannot withhold our conviction, after tracing the curves which the needles form within, on, and above the earth, that the globe is a magnet, i. e. that its axis is magnetic; and according to the law of magnetism founded by direct experiment, the North end is the attractive and the South end is the repulsive, or in plainer language, that the magnetic fluid or currents move to- wards the north, enter into the axis, through which they pass, then issue out from the south pole and encircle the globe to com- plete their circuit (as indicated by the direction of the needles, and illustrated by the arrows in the following sketch) ;—we ought to be able to trace their effects on all substances within the limits of our observations. If the earth be a magnet, as we have endeavoured to prove, it must produce the effects observed ; if it be not a magnet, it pos- sesses a property identical in its results to one; therefore all we require in our investigations is the knowledge of the law of these actions, as the name of the primary cause of the action cannot have a material influence on our researches. If we continue to call it gravitation, we must add to it a property which was not applied to it before, viz. polarity,—call it magnetism, and the term embraces all we require in astronomy as well as in geology. Let us suppose a bar, having been made magnetic, to be placed 8 in the axis of an artificial globe, if iron filings be strewed care- fully over it, the filmgs would become magnetic, and arrange themselves in curves like the magnetic needles on our globe, as shown in Plate I. The small magnetic ingredients do not con- verge to one mathematical point at each end of the bar, but to a space equal to the transverse section of the axis; and if this effect is produced by a current of subtile fluid, which may be conceived to emanate from one pole and to enter in at the other, penetrating the substance of the bar, and again to issue from its former outlet, as exhibited by the arrows in the above dia- gram, it is reasonable to suppose that the fluid will not be com- pressed more than the transverse size of the bar will require. Taking this simple principle of action as a guide, with its vari- ous consequences under different circumstances, we shall soon perceive that we not only account for the various phenomena of geology, but, in a word, al/ phenomena connected with terres- trial physics; and that we are enabled also to reason from the known to the unknown, and actually to predict facts before trial, not merely to satisfy curiosity, but questions of practical utility, especially in mining. Indeed, theories are not worthy of atten- tion unless they can be fairly demonstrated and rendered practi- cally useful. The theory of gravitation was founded solely on the observed effects, and not from any knowledge of the cause; but this mag- netical theory has been founded on both, and has the advantage of merging the whole into one simple system, which does not require any mysterious calculations to comprehend it, but only ordinary abilities with the exercise of common sense. To proceed with our subject, let us consider a bar which has been rendered magnetic by the fluid entering into one end, and issuing out at the other, to be placed on a centre, or float- ing on water, we find that it will preserve its meridional position if left undisturbed; it is therefore manifest, that by some in- ternal action the iron bar is rendered susceptible of allowing the fluid to pass through it only in one direction, viz. from the south to the north end of the bar. If we cut the magnetic bar into several pieces, what would be the result, supposing that by so doing we do not injure its magnetic susceptibility? Might we not reasonably expect the same phenomena in the separate parts 9 as when entire, viz. that the current would still preserve its defi- nite direction through the separate pieces as when entire? Such is the fact; each portion of the fractured magnet is a magnet perfect in itself, 7. e. each has a north and south end correspond- ing to their united position. Similar effects ensue from the sub- division of one of these fragments into any number, however great; and if reunited, by placing them together again in the same position, the result would be the same: that such would be the case is very evident, as the separation of the magnetic bar, provided it be effected without injuring its magnetic proper- ties, only diminishes the length of the channels, not changing or altering the natural direction of the currents imparted to it originally. A similar process of reasoning, derived from the same principle of action, will show that two similar poles must repel one another, and that two dissimilar poles must attract each other, owing to the tendency of the circulating currents to obtain a free passage. The intensity of the action of the currents must be as their density ; and if we assume that the whole of the circulating cur- rents round the magnet, within a certain limit, are converged into the polar focus, their intensity must increase towards that point, inversely as the square of the distance; like any other fluid, air, water, or steam, which may converge to, or diverge from, a central passage. Consequently we can determine the resultants of the forces which may act upon a magnetic needle when its centre is situated in different directions relatively to the axis of another magnet; and what will be its movements, and what its final position of equilibrium. As the sketches exhibit the various effects, and as the correctness of the above is so easily proved by very simple experiments, we need not enter into any tedious details, but beg references to the Plates for ocular demonstration, which it is hoped will be found more clear and explanatory than any written description. Let us proceed to examine the effects of a magnet placed in a globe, as shown in Plate I. In placing needles round this globe, we find them arranging themselves in the exact order which they keep on the terrestrial globe, both as to dip and direction; and as there is nothing to disturb them on the wooden globe, their positions in the curves 10 of convergence are uniform; their focus of convergence being equal to the transverse area of the magnetic axis at both ends. — We find in measuring the force along the magnetic curves, that it varies inversely as the distance; allowing for the influence of the earth’s magnetism and tracing the effects in a horizontal plane, we obtain the following law, viz. that the force varies in- versely as the square of the distance from the surface of the ball in the equatorial plane, and also in the meridian from the poles towards the equator; being the necessary consequences of the expansion and compression of the magnetic fluid surrounding it, as shown in the sketches. This is precisely the law of what is called gravitation, but the meridional variation towards the poles of the earth has been ascribed to the effect of a centrifugal force produced by the earth’s rotation. The assumed centrifugal effect of the earth’s rotation is also considered as the cause of the earth being an oblate spheroid. In the first place, a globe constituted and placed under similar conditions as our earth is, with its enveloping fluids, placed under the influence of centripetal and centrifugal forces alone, according to the well-known laws of physics, would not, nor could not produce the observed figure, much less the observed variation of attraction towards the poles. Its magnetism alone, without rotation, must necessarily com- press the poles, and also cause the inverse law of intensity in the enveloping fluids. . In order to show further, that there is no necessity for a rota- tory or a centrifugal force to cause, or at least to preserve an oblate spheroid in a similar body, let us take the moon for an example. She is an oblate spheroid, yet she does not rotate, 1.e€. on an axis situated within her body, because she always pre- sents the same face towards the earth. Had the earth continued to present the same face towards the centre of its orbit, it could not rotate, yet we find a body similarly situated an oblate spheroid. To return to our subject: we find that magnetism alone tends to form a sphere into an oblate figure, by the variable intensity of the currents on its surface, and that this effect is observed on our globe. If this be the primary agent by which all the substances of our globe are governed, we ought to be able to trace its effects according to the above principles of action, viz. circulating from south to north over the surface of our earth, ll with a force varying inversely as the square of the distance from the respective centres. Commencing with the atmosphere.—If the globe be a magnet, we ought to observe at the poles some in- dications of the convergence of the air towards the poles, 2. e. something similar to the inverted conical appearances which we observe in the ingredients at the poles of an artificial magnet, Plate I. It is true that the air is an invisible substance, yet, as it occasionally becomes saturated with visible fluids, it would, under such condition, with the advantage of reflected light, which may also be expected to vary according to the curves formed by the currents, show the phenomena of convergences. This fact we have in the aurora borealis and australis. These are the luminous appearances seen in the atmosphere connected with the poles of our earth, the general appearances of which corre- spond to the curves of convergence towards the poles. When these luminous phenomena display unusual brightness and ac- tivity, the magnetic needle is also found very fluctuating, both in dip and direction; and also the mercury in the barometer is subject to similar action; this coincidence of the variable move- ments indicates that they are produced by the same cause, viz. the disturbance of the equilibrium of the magnetic curves, or tension of the fluid. The aurora is not the cause of the needle being disturbed, nor are its luminous rays required to produce a rise or fall of the mer- cury in the barometer; on the contrary, the whole phenomena appear to be the effects of the oscillating movements of the mag- netic currents. The mercury in the barometer, like the magnetic needle, fluc- tuates without being accompanied with a visible aurora. Pro- bably the light is produced by a change in the constituent ele- ments; but the light is not essential to prove the existence of the currents; nor is visibility necessary to produce undulations in such currents: such variations can only be ascertained by their effects. That the barometer is subject to perpetual oscillation is a phe- nomenon so well known as not to require comment; but that the magnetic needle should be also subject to similar oscillations appears to those who have not paid attention to the subject some- what shtnge “Towever, the fact is, that the former is the effect 12 of the rise and fall, and the latter the horizontal movement of the same fluid ; the former is governed by the curves of equal density, the latter by the meridional direction of the currents. That there is a daily oscillation of the needle has been placed beyond a doubt by observations made with the most accurate instruments in almost every part of the world: the mean daily change amounts to about ten minutes. When the diurnal vari- ation of the needle was first discovered, it was supposed to have only two changes in its movements during the day. About 7 A.M. its north end began to deviate to the west, and about 2 P.M. it reached its maximum westerly deviation. It then returned to the eastward to its first position, and remained stationary till it again resumed its westerly course in the following morning. When magnetic observations became more accurate, it was found that the diurnal movement of the needle commences much earlier than 7 A.M.; but its motion is to the east. At half-past 7 A.M.in England it reaches its greatest easterly deviation, and then begins its movement to the west till 2 p.m. It then returns to the eastward till the evening, when it has again a slight westerly motion ; and in the course of the night, or early in the morning, it reaches the point from which it set out twenty-four hours before*. Within the tropics the variations in the height of the mercury in the barometer are very uniform, subsiding about half an inch during the day, and rising again to its former height in the night. In the northern regions, such as Denmark, Iceland and Greenland, the diurnal variations are greater and less regular, in the height of the mercury as well as the direction and dip of the needle; but in advancing from the north to the equator the di- urnal variations diminish. In the southern hemisphere the daily variation of the needle is in an opposite direction, the north end of the needle moving to the east at the same hours that it does to the west in the northern hemisphere. To give an ocular illustration, we may conceive the magnetic current as a string from pole to pole: if the string be drawn from its meridional position at the equator, its relative direc- tion or the angle formed between it and the meridian will be the same; but if we compare the direction on each side by look- * See Brewster’s Treatise on Magnetism. 13 ing towards the north alone, we shall observe that the bend of the string will be—say north-west in the southern hemisphere and north-east in the northern. That such should be the natural consequences of such disturbances is too evident to require further explanation. Besides these regular changes to which the needle and the mercury in the barometer are subject, they are often affected with sudden and extraordinary movements, to which Baron Humboldt has given the name of magnetic hurricanes, during which the needle often oscillates several degrees on each side of its mean position. The vibrating action of the needle during the appearance of the aurora is well known. It is also known that the luminous beams of the aurora are more or less parallel, or rather corresponding to the convergence of the dipping-needle ; that the rainbow-like arches are seen on either side of the me- ridian; and that the beams perpendicular to the horizon are only those on the meridian. It has been found that on the days when the southern aurore take place, the same phenomenon is observed also in the north: the one appears to be the cause of the other, and is therefore simultaneously produced, similar to the electric sparks seen at the poles of an artificial globe. Although the aurora lights are generally accompanied with oscillations of the magnetic currents, it is not necessary that they should always be so affected, because the light may arise from a change in the density or property of the currents, and not from any changes in their directions. That there is magnetic matter in the atmosphere is indubitable, and that this matter is con- stantly acted upon by the currents cannot be doubted. How- ever, it must not be expected that the variations are alike at all places, because the disturbances in the equilibrium of the mag- netic currents are influenced by various causes of a local nature. Resembling the weather in this respect, these variations may differ at different places at the same instant of time. The next point to be considered is the direction in which the magnetic currents move. If the currents, as we have previously stated, emanate from the south pole of the earth and enter into the north pole, we should expect somewhat different appearances in the south aurora compared with the north; because from the former they rise from an aqueous element, which must produce 14 a visible portion of vapour; and if so, the aurora will have the appearance of steam; whereas in the latter, as the currents de- scend from an aerial element, and are exposed to the effects of the sun, they must be drier. This difference has been observed by several navigators. The southern aurora consists of long columns of clear white , light, shooting up from the horizon, and gradually spreading over the whole sky. These columns are bent sideways at their upper extremities, and are in every respect similar to the northern lights, except in being always of a whitish colour, whereas the northern lights assume various tints, especially those of fiery and purple hue. The figure is identical—indeed exactly such as would be produced by the convergence, or vice versd, of the magnetic currents: and the difference in the colours is precisely what we should have been led to expect from the different nature of each pole. The saturated or hydrogenous nature of the currents coming from the south pole towards the north, will account for the observed peculiarity of the southern hemisphere in its gene- ral temperature, moisture, rains, the growth of vegetation, &c., as compared with that of the northern. The great ocean of air which envelopes the planet we inhabit, and to which we are every instant beholden for supplying us with the elements of vitality, is governed by the magnetic currents. Whatever substances may be decomposed and converted into gases, and rise in the atmosphere, are again returned into the earth by means of the currents. Nothing can be destroyed; on the contrary, whatever substances we may consume, reduce, or decompose, become again, by means of the enveloping mag- netic fluid, what they were before they existed, in the form of vegetable, stone or water, active agents in the business of the world, and main supports of vegetable and animal life, and are still susceptible of running again and again the same round, as circumstances may determine. CHAPTER II. THE IDENTITY OF MAGNETIC AND GALVANIC CURRENTS. AuTuHouGsH the sciences of magnetism, galvanism and electricity have been effectually blended, and proved by various experi- ments to be the effects of one primary cause, the direction of the magnetic currents compared with galvanic currents is con- sidered different, i. e. that the magnetic currents move at right angles to those of galvanism. This idea has arisen from the effects of the spiral course in which the external current that envelopes the connecting wire of a battery moves towards the negative plate. For instance, if the connecting wire of a battery be placed in the meridian, having its negative plate attached to the north end and the positive plate to the south, the external current enveloping the wire will move northward towards the negative plate in a spiral form. On the upper side of the wire it moves towards the north-west, and on the under side towards the north-east; on the western side it moves downwards, and on the eastern side upwards. This spiral nature of the current produces motion in a circular direction round the wire, which is exhibited in various electro-magnetic machines. It is there- fore very evident that the magnetic currents are not at right angles to those of galvanism. Supposing the intensity of the current causes the needle when held above the wire to deviate thirty degrees to the west, in placing it underneath the wire it will deviate thirty degrees to the east; taking the mean of the two, we find that the direction corresponds to that of the wire. That this is the fact is proved by making the experiment. It will _ therefore be observed, that the winding of a galvanic wire from east to west around an artificial globe, to illustrate the effect of the galvanic current on the magnetic needle, leads to very erro- neous conclusions, by presenting the direction of one side of the spiral and not the under one. The hypothesis of the magnetic currents being at right angles to the direction of the needles, must be admitted to have been 16 at best exceedingly strained and artificial, at variance with ana- logy of all other physical forces, and repugnant to our ideas of that simplicity which seems to pervade all the operations of the material world. All known forces, emanating from a certain point and exerted upon another point, act in the direction of the line joining these two points. Such is the effect of a stream of water on a substance exposed to its action, and on a vane by the wind, which always points in the direction of the current. The same law applies to electric and magnetic actions, in all the cases that belong exclusively to the one or to the other of these two classes of phenomena. , When two conducting wires, bent into helices, act upon one another, which they do in a manner that imitates very exactly the mutual action of two magnets, the action is called electrical, and is exerted in the lines of direction that join the acting points. The same is the case with two magnets in whatever position they may be placed. When the latter is exposed to the effects of the former, it indicates the spiral current above alluded to. All fluids, when forced through tubes by a great force, have a ten- dency to move in a spiral direction, as commonly observed in a funnel. However, if we take the mean of the direction of the spiral, we find that it corresponds to the direction of the wire; therefore we may safely consider that the magnetic needle, en- veloped as it is in the great terrestrial magnetic fluid, indicates the direction of the currents. We have now to prove that the currents move through the maenetic needle from south to north. In the battery we find that the currents of hydrogen move from the zinc to the silver plate, along or through the connecting wire. We find by ex- periments that the south pole of a magnet has a greater affinity for oxygen than the north pole. The difference in the oxidation of the south pole, compared with the north, is easily proved by various simple methods. All that is required is to place the ends of a magnet in water, and allow it to remain undisturbed for several days, and the fact is soon proved. A very powerful horse- shoe magnet will decompose water, and the oxidation will be observed to go on at the south pole, and the evolution of the hydrogen at the north pole: hence it is manifest that the currents move from the south pole to the north of the needle: the magnet ii possesses the property of filtering, as it were, the oxygen from the stream, be that stream what it may, such is the effect and such the direction of the current. Having so far shown that the magnetic and galvanic currents are identical, differing only in the degrees of intensity, the latter being somewhat confined to liquids, the former being equally active in the air, we shall proceed to trace the consequence of their action*. Before entering into the inquiry respecting the effects of the positive and negative poles of the great terrestrial battery on the surface of the earth, we shall first examine more in detail the action of Electro-magnetism, by experiments. CHAPTER III. ON THE REDUCTION OF METALS BY ELECTRO-MAGNETISM OR GALVANIC CURRENTS. WHEN metals are observed in rocks or veins in their metallic state, which is of common occurrence in metalliferous districts, persons are too apt to think that such metals must have been produced by some intense heat, similar to that applied in smelt- ing works. Such an idea arises more from the habit of our looking at metals as the production of our ordinary artificial process of reducing minerals, than to any cause that can be as- signed for this being the only mode of their formation. When we make a casting of any metal, even the most fusible, we find a great difficulty in getting it to take the exact impres- * Ritter asserted that a needle, composed of silver and zinc, had arranged itself in the magnetic meridian, 2. e. the zinc towards the south and the silver towards the north, and was slightly attracted and repelled by the poles of the magnet : to effect this the air must be very moist. Generally speaking, such needles can only act when immersed in liquid. In the air the needle must be composed of such substances as will be capable of decomposing that element to indicate polarity. It is a singular fact that those rocks which contain man- ganese combined with iron ore are the most magnetic, and will preserve longer their polarity. Cc 18 sion of the mould, owing to the great heat necessary to give the metal the required looseness and pliancy. The liquid metal has a considerable amount of cohesion, which tends to make it form into pretty large drops, like that observed in quicksilver ; which drops cannot be separated into smaller, or reduced with- out great force. Consequently there may be openings or hollows in the mould into which the melted metal will not easily enter ; and if these be very minute, it will be inadmissible. Besides, the substance which forms the mould must not only be capable of enduring a very high temperature, but sufficiently porous to allow the air to escape. The native metals which are found in mineral deposits are often enclosed in quartz ; but on whatever substances they may be, they present the exact impression, even the most minute : cracks of the mould. Nor are the substances on which such : metals are found always confined to those that resist intense heat; on the contrary, native copper and silver have been found deposited on timber, and decayed leaves in old mines. It is therefore very evident that the ordinary process by fusion is not capable of fulfilling the above conditions of the metals in the mines: but it is identical with those formed in the humid way by electro-magnetic action. In speaking of metals, we should not forget that a great num- ber of them are found not as solids, but in solution in the rocks. Indeed there is no rock 7m situ but is found more or less saturated with mineral waters. Tron is abundant almost in all mineral waters. Copper is found in solution in all the copper mines in Europe and America, and a large proportion of copper is obtained by the introduction of iron to precipitate the metal from its sol- vent. Other metals are capable of being in solution as well as in their solid state. Platinum remains in solution with one part of nitric to two of muriatic acid. Gold is soluble in nitro-muriatic acid. Silver is soluble in nitric acid. Nickel dissolves in nitric acid. Zinc, Lead, and in a word, all metals, are susceptible of remain- 13 ing in a soluble as well as a solid state ; therefore we should not consider that the metals must necessarily be solid in their ori- ginal state. Indeed there is some difficulty in preserving some metals, especially iron and zinc, in their metallic state, in con- sequence of their great affinity for oxygen; and those metals only which possess but little affinity for this element, such as platinum, gold, silver and copper, are found formed and pre- served in rocks in their metallic state. When we subject any metallic solution to the action of the magnetic current, the metal will be reduced, in different states, according to the strength of the solution and the intensity of the current. In order to ascertain experimentally what are the circum- stances which tend to produce these conditions, we have only to procure a galvanic battery and connect it with two platinum poles, which we place in a vessel to serve as the precipitating trough*. In this trough we place a saturated solution of a me- tallic salt—for instance, copper—when on examination, if the battery possess but feeble power, we shall find that crystalline copper will be deposited; if, however, we dilute this solution with twice, thrice, or four times its bulk of water, the metallic deposit will assume a very different aspect: it will then be ag- gregated in a flexible state, or a reguline deposit. If we now dilute this same solution to an infinitely greater extent, the metal will still be reduced, but in the form of a very fine black powder. Almost all metallic solutions may be substituted for that of the sulphate of copper, and the experiment will show nearly the same result, namely, that the strength of the metallic solution influences the nature of the deposit. If we examine the converse of the experiment, and take a so- lution of sulphate of copper, and use successively, first, one very small battery, then two or three batteries arranged in a series, and lastly, a very intense battery, we shall find that with this self-same solution we can obtain by these means, first, a crystal- line, then a reguline, and subsequently a black deposit. The above variable state in which minerals are deposited by * See Smee’s excellent work on this subject, Second Edition, p. 113. CG. 9 20 the battery is of very common occurrence in mineral veins; and even the same vein presents large and small crystals, and often of variable composition, within a very small compass. The application of the agency of fire to form such depositions, is not only a rude and clumsy hypothesis, but totally inconsist- ent with analogy, and contrary to facts: whereas a magnetic or galvanic current passing through solutions, if not the actual modus operandi of nature, is at all events capable of giving a ra- tional solution, not merely of the mineral veins, but also of all the operations of nature disclosed by geology. In order to understand how the metals are reduced from their solutions by the agency of a galvanic current, let us take a bat- tery, and endeavour to discover the cause of the actions there going on. In placing a plate of zinc in water, and allowing it to be im- mersed in it for a long period, it becomes coated with an oxide ; but if the water be diluted with sulphuric acid, the oxide will be dissolved, and the zinc will continue to present a clean surface to the oxygen of the water, until it is entirely dissolved, provided there be a sufficient supply of that element present. The above chemical action is however comparatively feeble. This feebleness of action appears to arise from the want of an- other power to take away the hydrogen evolved during the de- composition of the water by the zinc. If we place another metal having a less affinity for oxygen than the zinc in the same vessel, and connect the two by a copper wire, the action is considerably increased, and the hydrogen evolved from the decomposition of the water is apparently conveyed from the zinc by means of the connecting wire, and finally escapes from the surface of the plate which forms the negative. And it has been experimentally proved that the greater the facilities by which the hydrogen is made to evolve from the negative plate, the greater is the action on the zinc or positive plate. | The positive plate may be considered as the fuel of the bat- tery, and the connecting ‘wire, with its negative plate, the flue and chimney of the battery. If we increase the draft of the chimney for the escape of the decomposed air, the greater is the supply of oxygen to the fuel; if we break the connexion be- eo a oe a a 21 tween the fire and chimney by shutting the flue, we check the combustion ; and such is the nature of the battery. In order to increase the intensity of the battery Mr. Smee has introduced platinized silver, which possesses the singular pro- perties of evolving, or rather liberating the hydrogen with great facility ; hence the draft is thus increased, and consequently the combustion of the zinc accelerated. a QQ 35 Whatever may be the real origin of the current, it is very evident that its direction is from the positive to the negative plate, and that it is the positive plate alone which produces the action and causes the decomposition. It is not necessary to enlarge on this subject here, as the reader may refer to Smee’s admirable treatise on this interesting part of our inquiry. We shall only remark, that the metals in solution are reduced into their metallic state in the decomposing trough of the battery on the negative plate, 7. e. the plate which evolves the hydrogen, and apparently contrary to the direction of the current. But when we examine more minutely into the immediate cause of the reduction of the metal on the negative plate, we find that it is not produced directly by the current, but is the result of a secondary action; thusa solution of copper being subjected to a voltaic current, the hydrogen in oozing out of the negative plate seizes upon the oxygen of the oxide of copper, and forms water, whilst the metallic copper is thrown down on the plate ; and as long as the strength of the metallic solution is kept up and remains in contact with the plate, the hydrogen issuing out will continue to liberate the metal from the oxygen, and the re- duced mineral will present the appearance of a lateral growth from the plate. Whilst the above action is going on, on the negative plate, a contrary effect is taking place on the positive. If the positive plate of the decomposing trough be copper, as is always the case in reducing copper solutions, the acidulated water in contact becomes decomposed by the oxygen uniting to the copper, the quantity of copper reduced at this plate being about equal to that forming on the opposite plate, and thus the strength of the solution is kept up. Hence we observe that there is no real contrary current to 22 wards the negative plate; the effect being due to one con- stant direction in which the hydrogen moves, uniting with the oxygen at one pole, and becoming liberated from it at the other. We have already observed that the nature of the reduced metal depends on the intensity of the current and the strength of the solution. If the current be very intense, causing the evo- lution of the hydrogen from the negative plate, it forms a fine black powder; if none evolves, the metal is generally thrown down in its crystalline state. Mr. Smee observes, “that the quantity of electricity passing in a solution of copper curiously influences the state of the cry- stals, for there are two varieties of this deposit; one of which arises from a deficiency of quantity, relation to the strength of the solution, and in this state the new plate of metal is like an ageregation of sand, in fact like common sandstone, the particles having no more cohesion or consistence. In this state the plate of metal is in the utmost state of brittleness, and this, we must recollect, is produced by too small a quantity of electricity in a strong metallic solution. The second variety of the crystalline state of metals arises from a large quantity of electricity in re- lation to the size of the plate; thus, by using a very large posi- tive pole, connected with a battery of feeble intensity, and by employing at the same time a strong solution, large crystals, possessing the utmost degree of hardness, will be thrown down.” Comparing these facts with those observed in metalliferous de- posits, we find a very striking coincidence ; and when we apply similar laws and orders of deposition to mineral veins, the pro- blem of their formation is easily solved without having recourse to the igneous theory*. * Mr. Fox has obtained an electro-type copper plate by the agency of these subterranean currents. He found their natural direction to be from south to north in Pennance mine. After a few days crystals were formed in the nega- tive plate, but two months had nearly elapsed before the apparatus was removed from the circuit. 23 CHAPTER IV. ON HEAT PRODUCED BY THE MAGNETIC OR GALVANIC FLUID. THE next phenomenon which a battery displays is the power of heating substances according to the amount of current which is actually passing, and the resistance which they afford to its passage ; and in this way the most infusible metals, as platinum, palladium, gold, copper, iron and steel, may be instantly melted. Conducting liquids may be heated in a similar manner. This fact may be seen in a great variety of ways: dilute sulphuric acid may be made to boil in a siphon connecting two vessels, in which the poles of an extensive series of batteries are placed. Another mode of showing the same fact is to take a piece of string and moisten it with acid, connecting the extremities with the poles of a series of galvanic batteries, when it will begin to smoke, and become charred from the heat produced. The next property which a battery displays is its power of igniting metallic or charcoal points when joined to the two ends of the battery, and held so that they barely touch; a light is then exhibited equal in brilliancy to that of a little sun. The spark seems to depend principally upon a combustion of fine particles of metal, and, when charcoal or hard gas coke is used, upon little points of it flying from one pole to the other ; so that one pole wastes away and the other increases, till the flame be- comes quite encased in a mass of carbonaceous matter. This flame is singularly repelled or attracted by a magnet held in its vicinity. Heat is, indeed, one of the effects of chemical action ; and though we might by a fallacious reasoning be led to assert that chemical action is the effect of heat, a very slight examina- tion will show the absolute futility of such reasoning. In fact, we have no heat of which the cause is known, but that which is derived from, and proportionate to, chemical action. When we observe a body of water, we may with propriety state that it was derived from the ocean; but we could not be justified in attributing a similar origin to fire, or in stating that ya substances, when issuing out of the rocks in a melted state, must be the produce of an incandescent nucleus. We have only three primary divisions, viz. solid, fluid and gaseous: we have no in- dependent igneous elements ; the latter division is merely the effect of decomposition. Yet although this fact is so well known, the igneous theory is still pertinaciously adhered to. The word heat generally implies the sensation which we ex- perience on approaching a fire; but in the sense it bears in physics, it denotes the cause, whatever it be, of that sensation, and of all the other phenomena which arise on the application of fire, or of any other heating media. We should be greatly deceived if we referred only to sensation as an indication of the presence of this cause. Many of those things which excite in our organs, and especially those of taste, a sensation of heat, owe this property to chemical stimulants, and not at all to their actual heat. There are a number of chemical agents which, from their cor- roding, blackening, and dissolving or drying up the parts of some descriptions of bodies, and producing on them effects not gene- rally unlike those produced by heat, are said, in loose and vulgar language, to burn them ; and this error has even become rooted into a prejudice, by the fact that some of these agents are capa- ble of becoming actually and truly hot during their action on moist substances, by reason of their combination with the water which the latter contain. Fire, or the combustion of inflammable bodies, is nothing more than a violent chemical action attending the combination of their ingredients with the oxygen of the air. One of the arguments brought forward in support of the ig- neous theory, or central heat, is that it is found, by experiments in mines, that the heat increases with the depth, and that hot springs and mineral waters are found in all countries. Had this increased temperature proceeded from the radiation of an incan- descent nucleus, we should have a more uniform variation as we descend. In South America, where a great number of experi- ments were made, the variations in the degrees of heat were not — only very irregular and confined to particular patches in the rocks as we descended, but also in some instances the tempe- rature was found many degrees lower at a greater depth than near ? 25 to the surface. ‘This is easily accounted for by the variable na- ture of the chemical actions which are going on in the rocks. Parts of the rocks in deep mines, which are found intensely hot at one time, are at another time found at a very low temperature ; and such is the nature of the heat observed in all mines. That the intensity of action should be greater in depth gene- rally than near the surface, is a reasonable supposition ; but we have no proof of any intense decomposition or igneous effects taking place at those depths without the oxygen of the air or water being connected with such points. And if so, the decom- position of either element would be sufficient to account for any intense action taking place without having recourse to the hypo- thesis of central heat. All that we require to account for the observed geological phenomena is a current circulating within the crust of the globe, acting chemically and mechanically on those elements which form the external part. It is the opinion of some very profound geologists, that the globe was originally in a state of igneous fusion, and that as this heated mass began gradually to cool, an exterior crust was formed, first very thin, and afterwards gradually increasing, until it attained its present thickness, which they calculate as amounting to sixty miles. During this process of gradual re- frigeration, some portions of the crust cooled more rapidly than others, and the pressure on the interior igneous mass being un- equal, the heated matter, or lava, burst through the thinner parts and caused high peaked mountains. The same cause they allege produces volcanoes. According to this theory, we live upon a thin crust enclosing matter in a state of intense heat, which in particular districts agitates the earth in its pressure to escape, thus causing earth- quakes, or occasionally bursting forth and producing volcanoes. The arguments adduced for such a doctrine are the following: First. ‘That the form of the earth is just that which an igneous liquid mass would assume, if thrown into an orbit with a motion similar to that of the earth ; as if an aqueous liquid under similar circumstances could not eadisee the same kind of figure. Second. That it is found that heat increases with the depth in mines; thus inferring that there must be fire to produce heat ; whereas it is proved by experiments that chemical action is ie immediate cause of heat. 4 26 Third. They likewise argue, that the peculiar appearance of lavas all over the world indicates that they proceed from a com- mon source, These indications are merely that of a rock altered by a solvent, and that solvent, be it igneous or aqueous, is go- verned by the laws of chemical action, and therefore no argu- ment in support of central heat. Finally, they contend that on no other hypothesis can we account for the change of climate indicated by the fossils. In another chapter we shall endeavour to show an ample cause for the latter. Not only is the above doctrine of central heat unsupported by the arguments brought forward in its favour, but the conse- quence of such an igneous nucleus according to the laws which regulate the circulation of heat through fluid bodies, would be, that the crust of the earth, instead of increasing in thickness, would be altogether melted, even were it two hundred miles, much less sixty. (See Plate XX.) A cold crust and an incan- descent nucleus are incompatible, and contrary to the known laws of terrestrial physics; yet it has been attempted to show by experiment and mathematical calculations that these are ne- cessary truths in a body circumstanced as the earth really is. It is without doubt one of the most dangerous errors in every Science to attempt to allow mathematical refinement to usurp the place of careful experiment; and it would not be difficult to point out many instances of the injury which physical inquiry has sustained from the too-prevalent reliance upon the supposed power of mathematical investigations to alleviate the toil of in- ductive research; thus too often substituting the laws of geo- metry for those of physics, and leading the mind completely astray from the legitimate effects of the latter. To make the hypothesis of an incandescent nucleus appear somewhat consistent, the following experiment is suggested :-— “If one end of a bar of metal, a few feet long, be plunged in the fire, while the other end is wrapped in a wet cloth, the one end may be ignited to any desired degree, while the other can be kept at any required temperature above a certain point, depending on the heating and cooling powers applied to the ends of the bar, its length, and the conducting and radiating powers of the metal. Instead of the metal bar, submit to the same heat a bar of stone or a rod of glass; in these cases, unless the bar be very 27 short, no cooling power at all is needed further than that of con- duction and radiation from the surface of the bar, because of the extreme feebleness with which heat passes through its interior parts. What is the difficulty of applying this reasoning to the stony crust of the earth?” It is simply this, that heat is kept up by combustion, and that must be supplied with oxygen. Consequently that part exposed to the fire must necessarily con- sume and would finally decompose. Therefore a crust floating on an incandescent element under similar circumstances, as above described, could not increase, but would necessarily dissolve. The above bar should be placed on the fire sideways, to repre- sent the assumed condition of the crust. Such a doctrine deserves no serious attention, when we find that the observed phenomena are consistent with those pro- duced by chemical actions. If we admit the existence of sub- terranean currents, and that these exert a slow decomposing power, like that of the voltaic battery, we have a sufficient power for our purpose. In the first place, we have a mechanical ten- sion on the consolidated parts of the rocks, by the linear action of the currents passing through them; and should the intensity of the currents be very great, fractures would ensue, more or less at right angles to the direction of the force. These fractures would admit air and water, and thus produce intense heat, by the avidity with which the metallic nature of the bases of the earths and alkalies combines with the oxygen. That nearly all the substances which constitute the crust of the globe are found in solution as well as solid, saturated through- out the rocks, and to such a degree sometimes as to issue out and form springs, is well known; therefore, judging from the violent effects on a small scale which we are able to produce by experiments, a heat would be engendered quite adequate to occasion all that takes place in volcanic eruptions. It is a fact, that nearly all active volcanic groups are within a short distance of the sea; and even those that are situated at a distance from it may be connected with subterraneous channels of water. It is also a well-known fact in South America that fish are commonly thrown out of the crater, and some of the eruptions consist en- tirely of mud or muddy water, thus giving a still greater proof of their origin. The sudden fracture, as well as the sudden expansion of the gases, would produce a vibratory jar, which, 28 being propagated in undulations through the rocks or external crust, would give rise to superficial oscillations, and thus cause earthquakes. We shall note here a singular fact connected with the earth- quakes of South America, viz. during nine years’ observations made by the writer; the oscillations were from east to west, whilst the directions of their disturbances, and the rumbling noise which generally accompanies them, were from south to north. The former were generally confined to comparatively narrow limits, whilst the latter extended often from Chili to central America. This meridional action of the subterranean currents from . south to north is not confined to South America, but extends to the northern hemisphere. And it appears from numerous ob- servations made on the magnetic currents, that the power which governs earthquakes and magnetic currents is the same. The mean direction of the latter in South America corresponds to the average direction of the subterranean disturbances. CHAPTER V. TERRESTRIAL MAGNETISM, OR THE EFFECTS OF THE POSI- TIVE AND NEGATIVE POLES OF THE GLOBE ON ALL SUB- STANCES WITHIN THE LIMITS OF THEIR ACTIONS. From a consideration of the general facts that have been stated with respect to the effects of the galvanic current and its identity with magnetism, it will be sufficiently evident that the earth acts - upon magnetized bodies in the same way as if it were itself a magnetic battery; or rather, as if it contained within itself a powerful magnet or battery lying in a position coinciding with its axis of rotation. In order to make the above to agree with the facts as indi- cated by the needle and other bodies possessing the property of polarity, we must assume that the north pole of the earth is the positive one, as the currents are moving towards it, therefore the pole of decomposition, and the south the negative pole, 7. e. the pole of recomposition. Provided these poles be connected 29 by a conducting fluid an action would ensue ; and in consequence of the oxidation going on at the north pole there would be a ten- dency in the conducting element to move towards it. The ocean may be considered as the conducting element, its composition being peculiarly applicable for the purpose. The most general component parts of the sea, in addition to pure water, are muriatic acid, sulphuric acid, fixed mineral alkali, magnesia, sulphate of lime, and various other substances. We also know that the ocean reaches from pole to pole. On reference to the observations made on the general currents of the ocean, we find the following :— The principal currents of the Pacific, Atlantic and Indian oceans proceed from the south pole in a north-westerly direction towards the north. These currents are subject to numerous modifications, in consequence of the obstacles presented by the land to its free passage. The eastern coast of South America, _and the western coast of Africa form the boundary to the Atlantic ocean, and the general movement of the ocean between the above is in a north-west direction, until it enters amongst the West India Islands and the Gulf of Mexico; from which point it turns towards the north and north-east near Newfoundland. In the Pacific ocean there is a similar northward current. Another interesting question connected with these general northward currents is the fact, that within the Polar region the fruit of trees which belong to the American torrid zone is every year deposited on the western coasts of Ireland and Norway ; and on the shores of the Hebrides are collected seeds of several plants the growth of Jamaica, Cuba, and the neighbouring continent. The most striking circumstance, perhaps, is that of the wreck of an English vessel, burnt near Jamaica, having been found on the coast of Scotland. From the account of Captain Parry, it appears that there is also a great quantity of timber cast by the sea upon the northern coast of Spitzbergen. Timber is found floating in large quantities in the north polar seas, and much of which is thrown ashore on the northern side of Iceland; some of which appears to be of the growth of Mexico and Brazil. This question has engaged a good deal of attention, and has been con- sidered difficult to explain; but by admitting the general north- _ ward tendency of the ocean the question is easily solved. 30 ~ Ice is fallen in with much sooner im sailing towards the south than it is in approaching the north pole. The dry lands or the large continents are more or less pointed towards the south, whereas the northern parts are more or less ragged and crowded about the northern pole; in a word, all observed facts tend to prove that the ocean moves from the south pole towards the north. (Plate V.) If, then, such an action is actually going on in the great ter- restrial battery, its effects will not be confined to that of the ocean, but will also produce corresponding effects on the solid and semi-fluid part of the earth. Such an effect is apparent in the meridional lamination of the crystalline rocks, as shown in Plates IV. and V. In South America we find the whole region laminated in a north and south direction, subject of course to great contortions from various local disturbances. This lamination forms those kind of rocks known by the name of gneiss and schistose, being | in fact a modification of the granitic base, produced by the polar laminating action, and not, as it is erroneously considered, the result of a mechanical sedimentary action. The planes of these meridional laminations are generally more or less vertical, and are often seen cutting through sedimentary beds at right angles to the seams of deposition, and thus showing their independent and subsequent origin. Nor is this meridional structure con- fined to South America, but extends to the north, subject of course to great bends from numerous mechanical resistances. It may be considered strange that such an universal structure has escaped attention, and that it has not ere this been dis- covered. The isolated facts have been long known, but not properly used, and the laminated structure has been, and con- tinues to be, confounded with those planes resulting from mecha- nical deposition. As we have already noted, the granitic gneiss and the schistose, which are commonly represented in geological sections as sedimentary beds resting on one another, are the re- sult of a crystalline action modifying the granitic mass in the direction of the lamination, which structure is generally formed in a more or less vertical position as commonly seen when not disturbed. “« Since the year 1792,” says Humboldt in his treatise on Rocks, Se ee ee EEO 31 “T have been attentive to the parallelism of beds. Residing on mountains of stratified rocks, where this phenomenon is con- stant, examining the direction and dip of primitive and transition beds, from the coast of Genoa across the chain of the Bochetta, the plains of Lombardy, the Alps of St. Gothard, the table-land of Suabia, the mountains of Baireuth, and the plains of North- ern Germany, I have been struck, if not with the constancy, at least with the extreme frequency of the directions from south- west to north-east. This inquiry, which I thought would lead naturalists to the discovery of a great law of nature, at that time interested me so much, that it became one of the principal rea- sons for my voyage to the equator. When I arrived on the coast of Venezuela and passed over the lofty littoral chain and the mountains of granite-gneiss that stretch from the Lower Oronoco to the basin of the Rio Negro and the Amazon, I re- cognized again the most surprising parallelism in the direction of the beds; that direction was still north-east.” Unfortunately, in consequence of Werner’s theory, Humboldt wrote the above under the impression that the gneiss and schis- tose rocks were similar to sedimentary beds; hence he confounds the lamination of the former with the divisional planes of the latter. “ When we examine,” says M. Boué, “with a compass the position of mineral masses in Scotland, and endeavour to stop at general facts, we perceive that the direction of the beds is constant,and corresponds with that of the chains from south-west to north-east, but that the dip varies according to local cireum- stances.” According to Von Buch and other continental geologists, the directions of the lamination of the crystalline rocks in Sweden and Finland are from south to north, varying occasionally to- wards the east. In Mexico the laminated structure is princi- pally towards the north-west; but in the plains it is frequently found due north and north-east. In the United States its gene- ral direction is similar to that of South America, 2. e. from south to north, but presenting numerous contortions, and thus causing local variations in the direction, either towards the east or west, according to the nature of the local resistance. “The direction of primitive and transition beds ” (gneiss and 32 schist), says Humboldt, “is not a triflmg phenomenon of lo- cality, but, on the contrary, a phenomenon independent of the direction of secondary chains, their branchings, and the sinuosity of their valleys ; a phenomenon of which the cause has acted, at immense distances, in a uniform manner, for instance in the an- cient continent, between the 43° and 57° of latitude, from Scot- land as far as the confines of Asia.” Hence it will be observed that the universality of this struc- ture has not escaped attention. Dr. M‘Culloch, in his description of the Western Islands of Scotland, remarks on the striking uniformity of the beds of gneiss and schist being more or less in a north-east direction. In cutting any of these beds, as they are called, in an east and west direction, 7. e. from the eastern to the western coast of Scotland, the lamina would be intersected transversely, and on examination the planes would be found more or less vertical, sometimes leaning to the east and sometimes to the west: any east and west section of considerable length would be found the same. It must be understood, however, that the above remark is confined to the average, because numerous bends and contor- tions of very considerable extent are frequent in this fundamental structure, and are susceptible of constant changes from the effects of chemical action going on in it. On the eastern coast, between Waterford and Dublin, the more ancient lamination presents a mean average direction towards the north-east, but is also intersected at various points by a comparatively recent lamination in a north-west direction. It is at these intersections of the old and new lamina that the me- talliferous deposits of Ireland are principally found. In the Barony of Bantry the old laminated structure is much contorted and dislocated. In North Wales and the northern part of England similar oblique intersections of the old and new lamina are observed. The most recent lamination of Cornwall is nearly in the direc- tion of the magnetic needle, and corresponding to that of Wicklow. The above observations are not founded merely on a super- ficial survey of these districts, but on a laborious investigation under ground, as well as on the surface. Indeed, without studying . ———— eT eS ee eee ee ga the structure of rocks beneath the surface, where chemical actions are observed in operation, and various crystals constantly form- ing, it is not possible to arrive at anything like a correct know- ledge of the law which governs the superficies of our globe. In Auvergne the lamine of the gneiss and schist run nearly in a direction from south to north, and dip to the west, that is, when viewed on a great scale, for when examined more partially the ordinary exceptions occur. In short, the continent of Hurope exhibits. this uniformity of structure throughout. In the United States of America we find the same meridional structure. In Virginia the gneiss, talcose and chlorite slates run north and south, leaning from the perpendicular towards the west. The Boston railway exhibits, by its numerous cuttings in an east and west direction, the general verticality and meri- dional structure of the schistose rocks for several miles in length. Along the north coast of South America, in the Carribbean Sea and the West India Islands, the same structure prevails ; and was minutely examined by the author, from east to west across the three great branches of the Cordilleras, between the latitudes of 4 and 6 degrees north. In an admirable essay published on this subject by Professor Sedgwick, we find the following observations :— “In that variety of slate which is used for roofing, the struc- ture of the rock has been so modified that the traces of its ori- ginal deposition are quite obliterated ; and this remark does not apply merely to single quarries, but sometimes to whole moun- tains .... In the Welsh slate-rocks we see the cleavage planes preserving an almost geometrical parallelism, while they pass through contorted strata of hard slate, obviously of sedimentary origin .... Crystalline forces have re-arranged whole mountain masses of them, producing a beautiful crystalline cleavage, pass- ing alike through all the strata... . And again, through all this region, whatever be the contortions of the rocks, the planes of cleavage pass on, generally without deviation, running in parallel lines from one end to the other, and inclining at a great angle to the west .... Without considering the crystalline flakes along the planes of cleavage, which prove that crystalline action has modified the whole mass, we may affirm that no retreat of parts, no contraction in dimensions, in passing to a solid state, can D 3A explain such phenomena as these. They appear to me only resolvable on the supposition \that crystallme or polar forces acted on the whole mass in given directions and with adequate power.” In the Geological Report of Cornwall and Devon, Sir H. de la Beche remarks,— “When we regard the prevalence of the great divisional planes in particular directions crossed by others nearly at right angles to them, producing solids to a certain extent symmetrical, and consider the mineral modifications which the sedimentary beds have generally undergone since they were deposited, we are led to suspect not only that the lamination planes, commonly termed cleavage, are, as has been supposed by some authors, due to polar JSorces, but also that the great divisional planes have been equally caused by them, as has been considered probable by others.” “‘ Although the direction of the present magnetic meridian in the district may be merely temporary, and the proximation of so many great divisional planes to it therefore accidental, still their great prevalence, both in the igneous (crystalline) rocks and sedimentary deposits, in that direction, leads us to suppose that polar forces may have considerably governed the arrangements of the component matter of the rocks they traverse during con- solidation .... If we require a constant tendency of such polar Jorces to arrange the component matter of rocks during consoli- dation in given areas, we can the more readily account for the frequency of nearly similar directions in the great divisional planes of rocks of different ages.” These observations are quoted here merely to show the striking coincidence of independent investigations with which the writer was totally unacquainted during his researches in America; but they clearly prove the universality of the polar lamination. During a recent examination of the metalliferous deposits and primary rocks of England and Ireland, we found the old lami- nation of the United Kingdom, on an average, a few degrees east of north, and the new lamination intersecting it obliquely, in a direction approaching the present magnetic meridian. See Plate IX. The same kind of polar structure has been observed in coal beds in all countries. The meridional lamination has been observed from Morocco, in 30 the north of Africa, to the most northern parts of Kurope ; there- fore the crystalline crust of the earth does not consist of confused shapeless masses, resulting from igneous eruptions, but possesses a structure and arrangement of parts as regular and uniform as any other natural production. It has but one general grain, by which any of the masses will split, and that is from pole to pole, as represented in Plates IV. and V. This meridional grain is pro- duced by the polar arrangement of the crystals in the granitic _ base causing more or less vertical sheets or plates of mica, talc, chlorite, &c., the influence of which, together with the constant circulation of the polar currents in the direction of the planes, extends to the sedimentary beds, and thus the whole of the sur- face becomes uniformly cleaved. CHAPTER VI. ON THE GENERAL CHARACTER OF THE CRYSTALLINE ROCKS CALLED “ PRIMARY.” Tue first remarkable fact that presents itself to our notice on examining the nature of these rocks is, that they contain a very considerable proportion of water, and are often found in depth as soft as clay. Nothing is more common than springs, a great number of which are daily forming incrustations of mi- neral matter by precipitation. In New Granada great streams of siliceous and calcareous matter are seen issuing out of the rocks and forming large deposits. When the calcareous solvent happens to predominate, the silica becomes aggregated into small lumps, like flints in chalk, and when equal they form distinct beds. In mines and caverns mineral springs are very abundant, and numerous crystals are constantly forming, according to the strength of the mineral solvents. A crystal thus produced may with propriety be called “ primary,” as it is formed from a pri- mary element, like a crystal of salt from the sea, into a definite form, according to exact laws ; and the powder of such a crystal reconsolidated by any cement may be called a “ secondary ” or “sedimentary ” formation. Therefore the terms “ primary ” and D2 36 *‘ sedimentary ” rocks used here, are to be considered in the same sense, having no reference whatever to the time of their forma- tion. With regard to the interior of the globe below the “ pri- mary base,” nothing can be determined from immediate observa- tion, nor is the question essential to our inquiry. Were we to speculate on this subject, we should consider it filled with hy- drogen gas, from the fact of its surface being principally com- posed of water: be this as it may, there is no reason to suppose it to consist of an igneous fluid; we cannot conceive the exist- ence of such an element in a quiescent state. This point can- not be too much insisted upon, as geologists have assumed such an agent, and consequently a// crystalline rocks are called igneous. In our investigation of phenomena dependent on natural causes, certain laws of reasoning should inviolably be adhered to. First, no cause should be adduced whose existence is not proved either by its effects or by a true process of induction. Secondly, no effect should be attributed to a cause whose known powers are inadequate to its production. Thirdly, no powers should be ascribed to an assumed cause but those that it is known to possess according to the laws of terrestrial physics. To these rules we mean strictly to conform, in which conformity rest the merits of our argument in support of the effects of terrestrial magnetism to account for all geological phenomena. In the first place, we have no proof of the existence of an ig- neous element. Granting its existence, it could not produce a solid, but merely the melting of a substance already formed ; therefore there is nothing gained by such an assumed agent. Besides, it is extremely difficult to produce crystals from fusion, and those which are imperfectly formed are produced when in the act of sublimation. Siliceous and calcareous crystals have often been formed by art in the moist way, but never by igneous fusion. The crystals forming the primary base could never be imitated by fusion, even though every other necessary circum- stance should concur, especially those with or without an inter- mediate prism, terminating with pointed pyramids at both ends, as those of quartz and calcareous spar. Even those rocks called ancient lava, such as basalt, trap, &c., are of the same aqueous composition as any other rock, their pores being always filled am with mineral salts. There is not a single case to support an igneous doctrine ; whereas by means of the natural solutions and the polar current, we can, not only account for, but imitate the natural productions. There is scarcely a substance known but what is either found naturally in solution, or-may be dissolved in an aqueous menstruum. The apparent insolubility of quartz has given rise to some of the difficulties which have embarrassed geologists; but as silica is found in that state in the primary base, we need not trouble ourselves with the question how quartz may be redissolved. We shall consider the ocean as the primary menstruum from pole to pole,—a compound of all the elements in solution through which the magnetic currents circulate. From analogy and by experiment, crystallization would commence at the ne- gative pole, and would continue to form until its growth would extend to the positive pole in meridional lines, thus producing the polar grain or lamination explained in the previous chapter. In the primary rocks we recognise in every crystal the action of the constant and undeviating laws of the polar force and che- mical affinity, giving to the mass a regular grain, and to every crystal a definite form and composition. Hence the above may be considered an experimental and natural truth. The elementary substances entering into the composition of the primary rocks may on an average be considered the following :— Silica, Iron, Aluminum, Manganese, Magnesia, Fluoric acid, Potash, Carbonic acid, Soda, Water. Lime, These are united with variable proportions of the gases, hydro- gen, oxygen, chlorine, &c. The compound consists of the above in a state of fluids, semifluids and solids, being an aggregation of the separate elements in different states of crystallization. Silica forms aes yee EEE Quartz. Silica, alumina, lime and potash . . . Felspar. Silica, alumina, potash and iron. . . . Mica. Silica, magnesia and potash . . . . . Tale. Silica, alumina, magnesia and iron . . . Chlorite. 38 Silica, alumina, magnesia, lime and iron . Hornblende. Silica, alumina, magnesia, potash and iron Schorl. Lime and carbonic acid . . . . . . Carbonate of lime. Besides the above compound ingredients, there are also dis- seminated in the primary mass all the known mineral substances ; these may likewise be compounds, of which hydrogen forms a part. Granite may be considered as the fundamental crystalline base, a compound of the above ingredients in variable propor- tions. Numerous appellations have been from time to time sug- gested for the different kinds of granites, but it is very evident that such distinctions cannot be established, inasmuch as the variety of crystals constituting the granitic masses are very ir- regularly disseminated, and possess no distinct lines of demar- cation. However, in order to have some idea of their variable character, the following may be enumerated as very common compounds in Europe and America :— Micaceous granite. . . . Mica predominating. Chloritic - 42. eo) BRonlerte 35 Talcose ss SS eee ane 35 Hornblendic,, . . . . Hornblende ,, Quartzose ,, peu Cepheid 24012 1g 172 45 Felspathic ,, ete) ) elspa <5 Porphyritic ,, . . . . Felspar in excess with crystals of felspar in a base. Felspar in general constitutes by far the largest part of gra- nite: it is often in a soft and fluid state, and in small and large grains. The following varieties of granitic rocks are often associated in the same mountain mass, and may be regarded as contempo- raneously formed, accidentally modified by an admixture of dif- ferent ingredients :— Common granite; the felspar white or red, composed of quartz, felspar and mica. Chloritic granite; quartz, felspar and chlorite. Felspathic granite, in which felspar is the principal ingredient, and the quartz, and particularly the mica, very rare, with large erystals of felspar. , es 39 In these masses are veins of the predominating substances of the enclosing rocks. The granite being the fundamental base, or the crystalline shell of the globe, its thickness is not known. It has a polar structure, and when the quantity of mica is considerable, granite divides into parallel plates, or in other words becomes laminated, and exhibits the meridional structure explained above. Gneiss is the laminated part of the granitic base, the same identical mass; the distinction being produced by the ingre- dients tending to arrange themselves in parallel plates ; quartz follows quartz, felspar follows felspar, and mica follows mica. (See Plate VI.) As this crystalline arrangement and lamination of the funda- mental base is produced by the continual circulating action of the magnetic currents through the semifluid mass, the transi- tion of the crystalline aggregation to the laminated structure is necessarily insensible; the action being like a simultaneous growth of the granite northward. Hence a micaceous granite produces micaceous gneiss, chloritic granite chloritic gneiss, &c. Schist, or Crystalline Slate.-—This variety forms the termina- tion of the granitic base, the branches and leaves, as it were, of the great granitic trunks. The mica granite passes first into gneiss, and the latter into mica schist by an almost imperceptible gradation. This rock has been. represented as stratified by a mistake in confounding the stratified with the laminated struc- ture. (See Plate XVI.) It is the final decomposition of the fel- spar that distinguishes slate or schist from gneiss. (Plate VI.) It will therefore be observed that the primary crystalline, from the granite to the schist, belongs to one formation, and is essentially composed of the same minerals, variously modified by the polar force, and passes by insensible gradation from the base to the final slaty structure in a more or less vertical and meri- dional direction; but subject to constant changes and disturb- ances from local causes. These rocks are very extensively developed in South America, and may be traced from Chili to the Caribbean sea. A section was taken across the three Cordilleras, where the rocks were seen cut by ravines upwards of 2000 feet deep, thus exhibiting na- tural sections, and showing the nature of their transition vertically 40 as well as herizontally ; the minute, and very laborious investiga- tion of which is the foundation of the present observations. The crystalline series in Europe falls into insignificance when com- pared with those of America, and it is in such extensive areas that the real character of the crystalline base can be clearly as- certained. Besides the regular transition of the crystalline base into slate, there are also veins formed, interlaminated in the mass. Should the base contain a large proportion of magnesia and talc, veins of serpentine rocks will be formed; should the granite predo- minate in silica, quartz veins will be found very abundant. The felspathic granite never produces slate for the want of mica, therefore it is generally covered by a massive rock which is erroneously called clay-slate. Should hornblende and lime be disseminated in a felspathic base, hornblende, basaltic, trap, and greenstone veins are formed; and as carbonic acid is generally combined with the ingredients, this compound base produces great disturbances in the superincumbent masses; it is the most restless base of the whole of the above compounds. However, we must always bear in mind that there 1s no granitic base in situ actually dormant ; these are constantly acted upon by the polar current, with variable degrees of intensity. The porphyritic granite is the richest base for producing minerals in Chili, Peru, Quito, New Granada, Mexico, England and Germany. The quartzose granite is the most unproductive. When the granite forms a moist massive base it is seldom de- ficient in mineral salts, but when comparatively dry, with a di- stinct crystalline grain, it is generally poor in mineral. These are the primary points to be first considered in making a survey of a mineral district. The metalliferous parts of Cornwall have a porphyritic gra- nite, which on the surface is partially decomposed, forming patches of dark masses of the same substance ; the intermediate part (forming the transition) is called “ elvan,” being a fine grain porpyhry. The transition of the granite into the slate is very irregular, owing to the excess of felspar and the want of mica: this is also the cause of the series not possessing the uniform cleavage struc- ture seen in America and other places. However, there are a 4] few meridional channels intersecting Cornwall, presenting the usual phenomena of the vertical polar cleavage, and cleaving the superincumbent beds, which may be seen at the United Hills, St. Agnes, and various other parts of the northern coast. The interlamination of the granite, porphyry, and slate, and the com- mon northward transition, may be seen at Dolcoath, and along the whole range of the Carn Brea granite on the north side. The gradation of granite into gneiss, and gneiss into mica and _ clay slates, may be seen in Wicklow, and also in the western part of Scotland. The Irish crystalline series may be consi- dered as the southern extremity of those of Scotland. It has been conjectured that the slates of the western part of North Wales formed the eastern edges of those seen in Wicklow ; this idea originated from the mistaken notion that primary schist were sedimentary beds. The Wicklow and North Wales cry- stalline slates are two independent meridional series. (Plate IX.) A variety of talcose, micaceous and chloritic schists may be seen near Holyhead and on the south-west coast of Carnarvon, pessessing that fibrous structure and silky striated and shining lustre in the planes of the laminez or meridional cleavage, so peculiar to all the crystalline rocks. To enumerate the localities of the primary series would be an endless task ; therefore we must refer to other works, and confine ourselves to the mode of their formation and general structure. As the action in the primary base is constant, like a series of channels growing northward, with their pores and cleavages full of mineral solutions, subject to variable tensions, fractures, &c., the structure of the compound becomes occasionally very com- plicated, by which cause the phenomena of heaves, splits, veins, &c. are produced. Metalliferous rocks.—These are channels of rocks in which minerals are so abundantly disseminated that the whole masses are worked like quarries. In the silver mines of Mariquita na- tive silver is commonly found in flakes, like niica in the laminze of the schist, in channels of ground of about twenty-four feet wide, of course in the meridian, like the formation of the rock itself ; and these metalliferous channels are quarried for silver. In the same neighbourhood the argentiferous channels are very numerous. At Ibague, copper is found under similar circumstances in a 42 clay-slate formation ; ae lead and iron pyrites, i In porphyritic rocks in the same locality. Gold is principally found as a superficial efflorescence on the face of rocks and in cavities, seldom or never in a close grain or compact rock. It is found in the Brazils, Chili and New Gra- nada, in the tender part of porphyry and clay-slate. It is the destruction or waste of these friable rocks that produces the rich alluvial soil of America. The porphyry of Cornwall contains nests of yellow copper ore varying from a few ounces to several tons’ weight. In North Wales and Cumberland similar metalliferous rocks are common ; they are also very abundant in Ireland. | Moss copper is well known to miners: it is the produce of a metalliferous rock, out of which it vegetates like common moss. Gold, silver, pyrites, lead, and indeed all metals, may be seen occasionally growing out of rocks where the situation and cir- cumstances are favourable for their formation. The minerals are found in the rocks in solution as common as in the solid, indeed it is the state in which we consider them to be previous to their crystallization. All rocks are more or less impregnated with mineral solvents. The cupreous springs are very abundant in Chili, Peru, New Granada, Cuba and New Brunswick: they are to be seen also in Ireland, Anglesea, Spain and Hungary. The copper in solution is obtained by precipi- tating it by means of iron. The bog-iron ore is of similar origin, and is formed precisely in the same manner as the calcareous and siliceous tuffa. + Ty 43 CHAPTER VII. ON THE ORDER OF THE SPLITS, FRACTURES AND DISLOCA- TIONS IN THE PRIMARY ROCKS, INCLUDING THE SUPER- INCUMBENT SEDIMENTARY MASSES. AccoRDING to the meridional structure of the globe described in the preceding chapters, the general appearance of the surface may be compared to the grain of a fruit; such for instance as an orange or melon, having a grain from pole to pole. Indeed, when we look at the moon through a telescope, and especially in the clear atmosphere of the tropics, she also presents such an appearance. We observe numerous luminous rays radiating from the pole facing the south, which are seen diverging towards her equator, some of which extend to the northern edge *. Pro- bably the external part of all fruits, possessing two opposite poles, is formed in the same manner as the crystalline shell of our globe. This meridional action, producing the crystallization, fibrous and laminated structure of the consolidated masses, must neces- sarily cause a very considerable tensional strain. Let us, for example, suppose a given area were undergoing elongation by _ the polar force ; should any part of the mass not possess suffi- cient tenacity to allow it to extend, fractures would ensue, and those would take place more or less transversely to the direction of the force; the nature and number of these ruptures would depend on the variable state of the mass. Should the rock con- tain subordinate channels of unequal elasticity and variable width, splits would occur longitudinally or diagonally to the grain, ac- cording to the direction of the least resistance. That the rocks are elastic and subject to undulating motions, capable of being elongated, and not, as is too commonly supposed, a rigid incom- pressible mass, is a fact which we need not further insist upon. We have therefore the following series of lines as a necessary * The bright polar focus is considered a volcano by the Plutonists, and the ra- diating rays streams of Java; it requires no ordinary stretch of the imagination to suppose such conditions without causing some awful catastrophes. . 44 consequence of the polar action, viz. meridional grain or lamine, splits, and transverse or east and west fractures. Besides these, numerous smaller fractures must occur according to circum- stances; but as they are of minor importance and of a local character, we need not take them into consideration. We have already shown that the polar grain is universally observed ; the east and west fractures intersecting this structure are seen in the Brazils and Chili, forming immense veins of quartz. In Peru and Quito they are very abundant. In New Granada, on the western Cordillera, which is principally formed of porphyritic granite, the east and west fractures are very numerous, and are generally filled with quartz and auriferous pyrites, being the principal metalliferous solvents of this chain. The central Cordillera is very schistose, thus possessing great tenacity and capable of being elongated ; consequently the trans- verse fractures are but few, and confined to subordinate gra- nular channels: the longitudinal and diagonal splits are of or- dinary eccurrence, the sides are commonly grooved and highly polished by friction caused by the meridional movements of the parallel masses. The hornblendic, calcareous and talco-mag- nesian varieties are found extremely active in the above series. The eastern Cordillera is very quartzose, therefore the east and west fractures are very numerous, and are intersected by a few polar splits, with striated and polished sides. In Mexico the porphyritic variety predominates, and the meridional splits are consequently intersected by a great number of fractures. (See Plate VII.) In Cuba and the other large islands of the West Indies the same phenomena are observed. In the southern de- partments of the United States, and especially at Virginia, the polar splits predominate. These splits have cleaved the coal. beds of Blackheath into longitudinal fragments, causing great disorder in their position. (See Plate XVI.) In Cornwall they are very numerous; the splits are known by the names of fluccan and cross courses (Plate VIII.), and the transverse fractures are called Jodes. It is in the fractures that the mineral wealth of this county is found. The great polar splits of Cornwall and Devon extend across the Bristol Channel to Wales, and have cut the coal fields and all the sedimentary rocks of the province into meridional strips. 45 The same kinds of splits and fractures are seen throughout Kn- gland, Scotland and Ireland, and have broken the great sedi- mentary beds into various fragments of a somewhat rhomboidal form, according to the oblique angles of the splits. (Plate IX.) On the continent of Europe similar series have been observed, especially in Tangiers, Spain, France, Germany, Hungary and Sweden; we need not detail them, but beg reference to works describing each district. These splits and fractures, and their being in continual motion by the constant action of the polar force, produce great disorder in the general structure, and cause dislocations in the order of the masses (called heaves by the miners). These are the effects of the horizontal or diagonal motion of the individual strips of rocks between the splits from their original position. The great heaves are produced by the northward action of the rocks be- tween the polar splits; the sizdes observed in the east and west fractures are few, and generally insignificant; they are the effect of wedges of rocks squeezed between great splits. (Plate X.) These dislocations have created great discussions, and have caused very opposite opinions, owing principally to the impossi- bility of restoring the continuity of ali the fractures on both sides of the splits. A very little reflection must show that such an agreement in all the fractures could not be expected. In the first place, the ruptures across the splits would necessarily take place in the direction of the least resistance, be that in a direct line or not; it does not follow that it should be straight across the split. If, again, we consider that the rocks are exposed to the continual action of the polar current, and therefore subject to a slow movement northward, there would necessarily be frac- tures taking place periodically in the same masses, 2. e. when the “heaves” are only 1, 10, 20, 30, 50 feet; how then would it be possible to restore the continuity of the whole series of fractures ? It is well known, and can be proved, that the fractures have occurred at different periods. It is like attempting to refit pieces of ice, after having been broken and subjected to repeated move- ments and reunited again by repeated freezing, as to try to re- store dislocated masses of rocks in the primary base. When we consider the semifluid nature of the masses, and their permitting a continual molecular action through their pores in the 46 meridian direction, like the current of sap in a living tree, we _need not be surprised that the wall of the fractures, cannot al- ways be refitted ; their ruptured sides are altered by the chemical action in a very short time ; the southern parts of which are often seen penetrating into the northern by a new cleavage formed sub- sequently to the filling of the cracks, as represented in Plate XI. Miners are well aware that the sides of veins often bulge out in defiance of all mechanical resistance: it requires a consi- derable practical knowledge to keep them open to extract the mineral, particularly in very wet ground. When the splits happen to be in a north-west direction, the masses of rocks on the western side are generally forced northward more than those on the eastern side: if the splits be towards the north-east, the contrary effect takes place; that is, in real heaves, because a great number are called “ heaves ” that are only apparent. (Plate XII.) In Cornwall the majority of the splits are north-west, as described in Plate VIII. : consequently all the principal “heaves” of the country are to the right, the western masses having shifted northward more than the eastern. The red sandstone and carbonaceous series, intersected by a split near Tiverton in De- von, has been shifted northward on the western side nearly half a mile. In the vicinity of Tavistock and Callington similar northward movements are observed. There is another great northward “heave” near Redruth, produced by the great cross course traversing the North Downs. The direction of the ‘heaves ” is generally expressed by right and left, because the same expression serves on approaching them on either side. Some suppose that the nature of “heaves” depends on the direc- tion and inclination of the mineral veins or transverse fractures ; but this is a mistake: the movements of the masses are quite in- dependent of the cracks, and would be the same had they not ex- isted. Nor does it follow that the dislocated veins should be always “heaved ” on the side of the obtuse angle, as generally supposed, because this depends on the angle of the fracture itself. (Plate X.) The cause of the above order in the dislocated masses is made manifest when we examine the nature of the mechanical disturb- ance. Admitting the magnetic force to act in the meridian, the direction of the oblique splits destroys the parallelism or uni- formity of the polar forces; consequently the masses presenting ay the largest transverse bases to the south will be propelled north- ward at a greater rate than the others. (Plate XII.) Having lately made a very extensive investigation of the prin- cipal mines of Cornwall, Wales and Ireland, with a view of in- stituting a comparison between them and those of America, this part of our subject was carefully attended to, and the result has fully confirmed our previous opinion that the greater number of the veins on the large scale have been “ heaved ” and filled simul- taneously. The splits, generally speaking, are older than the transverse fractures. The mines of Flintshire are referred to as one instance out of hundreds which may be mentioned, where the transverse cracks are confined within the limits of the me- ridional strips. The cause of the meridional splits intersecting the east and west cracks is not from their being of a more recent origin, but owimg to one series being subject to perpetual lon- gitudinal movements, and the other to transverse actions. CHAPTER VIII. MINERAL VEINS, THEIR MODE OF FILLING, AND THE GENERAL CHARACTER OF THEIR CONTENTS. “4 Bes1DEs the conflicting opinions respecting the origin of mine- ral veins, much confusion has also arisen from the very loose signification which is given by miners to the term vein or lode, which they apply, in fact, to almost any species of mineral de- posit which affords a foundation for mining operations, however widely it may differ from the definition of these terms in a me- chanical sense. To avoid this confusion, and to render the opi- nion which is here maintained respecting their origin more clear, we shall distinguish them by veins of fractures and split veins ; the former being more or less east and west, and the latter north and south: transverse fractures and meridional splits are to be considered as identical. We must always bear in mind the fact, that the rocks are more or less strongly saturated with minerals in solution, in a state favourable to chemical action, and having a free motion through the pores of the rocks in obe- 48 dience to the polar force. Those who may wish to know whe- ther this is a known fact in England may consult the numerous experiments of Mr. Fox, who has proved the existence of the subterranean currents and mineral salts in Cornwall by repeated experiments. Indeed, to doubt this is equal to doubting the meridional action of the magnetic needle; the latter is the effect of the same power. We have already observed that the meridional channels of rocks contain different kinds of minerals, the fractures intersect- ing which form what are called lodes or mineral veins; we shall now consider the nature of their contents. The Filling of Veins. Agreeably to the preceding observations, we should naturally conclude, that if fissures be formed in a rock of any given che- mical composition, the pores of such a rock being filled with solvents, the fissures traversing it would contain the predomi- nating mineral substance: hence we should find in limestone, veins filled with carbonate of lime; in siliceous rocks, veins of quartz; in hornblendic granite or slate, veins of hornblende, &c.: consequently those veins which may intersect a series of rocks varying in their chemical composition, would be filled with a corresponding variety of minerals. Should the laminze or pores of any given channel of rock be more strongly satu- rated with mineral salts than another, the traversing crack, or a series of cracks, would be found to contain rich deposits oppo- site to, and within the limits of such a channel. This variation in the contents of the bounding rocks produces a corresponding variation in the fissure: hence the cause why the minerals are formed in isolated masses (called “bunches”, a well-known fact in every mining district. (Plate XV.) The reality of the depend- ence of the masses of metallic ores in a continuous vein upon the qualities of the bounding rocks, is very perfectly demon- strated by facts long known in England. Some veins of fracture change so much in their horizontal direction as to be considered in one part a ¢in lode and in an- other a copper lode. This is particularly the case with Chase- water lode, which at Wheal Daniel is called a tin lode, at Chase- water mine a tin and copper lode, and at Treskerby a copper lode. 49 The nature of the minerals and the accompanying matrix changes with the changes of the rocks intersected by the fracture. In South America the veins of fractures are also often found,—in one part auriferous, in another argentiferous, again cupriferous, according to the metalliferous character of the bounding rocks (Pamplona, Ibague). The changes in the contents of fissures, when traversing sedi- mentary rocks, are equally striking. The mining districts of Aldstone Moor, Teesdale, Swaledale, &c., consist of sedimentary beds of shales, grits and limestones, traversed by fractures; the minerals in the fissures are chiefly found opposite the limestone beds, which in the above district are the most metalliferous. (Plate XV. fig. 3.) The ore is more abundant in the limestone than in the gritstone, and in the shale ore seldom occurs. The matrix of the vein as it passes through the gritstone is often sulphate of barytes; but when it enters the limestone it changes to carbonate of barytes. When the rock on one side of a vein is thrown up or down considerably, so as to bring a stratum of limestone opposite a stratum of sandstone, or when the walls of the vein are of two different kinds of stone, the vein is never so productive in ore as when both sides of the vein are of the same kind. The connexion of the opposite beds of limestone appears essential to keep up the crystallising action, and consequently the accumulations of the useful metals from side to side within the fracture. When the strata are but slightly shifted, the com- ponent parts, or the elements of each stratum, connect the oppo- site walls obliquely: sometimes the shales cut through the veins from side to side; thus the transverse section of the contents of the fracture exhibits the order of the sedimentary demarcations of the bounding rocks, as shown in Plate XV. This important fact alone is sufficient to invalidate the idea of veins having been filled from above or below ; and proves very clearly that the veins of fractures have been forced open and filled gradually by a late- ral crystallization from the bounding rocks. In Derbyshire the beds of metalliferous limestone are inter- stratified by hornblendic rocks, called toadstones. When a vein of lead is worked through the first limestone down to the toad- _ stone, it ceases to contain any ore, and often entirely disappears : on sinking through the toadstone to the second limestone the E 50 ore is found again, but is cut off by a lower bed of toadstone, under which it appears again in the third limestone. In some situations, where the beds of limestone are divided by seams of clay, they cut off the contents of the vein as effectually as the teadstone. (Plate XV.) With regard to the metalliferous beds or channels of rocks, it matters not of what variety they are, provided they be good con- ductors and well charged with metallic solutions. The changes in the contents of veins intersecting the more or less vertical channels of the crystalline rocks are similar to those observed in the sedimentary rocks. The mining districts of Gwennap, Redruth and Camborne (Plate ViII.), consist of crystalline channels of clay-slate, por- phyry, greenstone, granite, &c. When the lodes intersect the pale-blue massive clay-slate, they are generally productive in copper, and tin in the chloritic variety. When the channels dip towards the east or the west, the bunches of ore dip in the same direction. If the channels of ground be very dry and of a close crystalline grain, they seldom produce minerals. The metallife- rous character of the channels depends principally on a primary porphyritic and moist base; this kind of rock appears to be the richest soil, as it were, for the production of minerals. These crystalline channels of rocks being more or less in the meridian, as we have already explained in a previous chapter, and the frac- tures called lodes intersecting them from east to west (Plates VII. and VIII.), each fracture will contain similar deposits of mineral in the same meridian, or in a line approaching to it, as illustrated in Plate XV.: hence the miner’s old rule in Corn- wall, parallel lodes produce parallel bunches. This is an esta- blished fact in all mining districts ; but it must be remembered that the rule cannot hold good in split veins. The east and west cracks being across the meridional grain, are exposed to the whole crystallising action of the series, whereas split veins be- tween the channels can only receive such solvents as may pass longitudinally through them: this is also the cause of the con- tents of the two classes of veins exhibiting a different structure, viz. the east and west from side to side, and the splits in longi- tudinal plates. (Plate X.) In order to exhibit the mode of filling, and the formation of a | different crystals in the same fracture, place a mass of clay-slate between the poles of a battery, immersed in a metallic solution ; it will be seen that the currents pass only in the direction of the cleavage: if the slate be broken across, so as to represent veins of fractures, crystals will be observed to grow in each fracture transversely, z. e. in the direction of the cleavage planes*. If two or more metals be combined in the solution, and the current be very feeble, only one of the metals will be formed in each crack at atime: should the current be increased beyond that required for the decomposition of one of the metallic salts, the others will be reduced proportionably and accordingly to their relative ease of decomposition. The intensity of the current and the proportion of the metallic salts may vary periodically, which may account for the variety of crystals irregularly grouped to- gether in the same vein and at the very same spot. When the intensity of the currents is very feeble the crystals are large, and when greater than sufficient to reduce the metallic salts, hydro- gen will evolve and the metals will be precipitated in a massive powder. Hence, when minerals are found in their metallic state and in large crystals, they indicate feeble currents, and conse- quently unfavourable for the production of large quantities in such veins. The most favourable indications for rich deposits are strong solutions of minerals, dammed by fluccans or clayey veins, so that the excess may ooze out on the surface, forming hydrous oxides and sulphates. The amount of deposition in each fracture depends on the mechanical position, as illustrated in Plate XIV. The most favourable position of a fracture for the accumulation of minerals is at right angles to the grain of the district, and shghtly dipping northward; the unfavourable frac- * We have already insisted that cleavage planes are formed in the direction of the currents from pole to pole. Experiments have been made with the view of imitating these crystalline planes, by placing a mass of clay between the poles of a battery, and it has been supposed that the small transverse fissures produced by the tension represent the phenomenon of cleavage. A very slight examination will show the distinction between them. Those who may feel disposed to imitate real polar laminze must furnish each pole with a piece of laminated rock ; without this preparation cleavage planes cannot be produced by artificial means. A mass of clay jammed between the walls in a vein of fracture will be cleaved across by the natural magnetic currents in a very few years. It is this constant cleaving action which is the cause of veins becoming obliterated, as represented in Plate XI. 1 52 ture is, that dipping southward at a flat angle under a heavy hill. In a series of parallel fractures the bunches of mineral will be found in a more or less meridional direction (Plates VII. and VIII), on the south somewhat deep, and on the north shallow deposits. This rise of the metalliferous currents varies in South America from 10° to 20° from the horizon. In Mexico the richer bunches of minerals are found in the parts where the fissures intersect the moist porphyritic varieties of clay-slates. (Plate VII.) In New Grenada, Peru, Chili and the Brazils, similar channels of rocks are equally productive. In a word, every mining district have their conducting metalliferous chan- nels, and the whole accumulated evidence obtained in all parts of the world clearly proves the fact, that the contents of the veins of fractures depend on the character of the rocks they traverse, as represented in the sketches. It is of great importance to bear this fact in mind, because veins which have been particularly rich at one place have led persons to suppose that the continuation of the same fracture must lead to more riches, although such a fracture may intersect barren rocks. Every mining establishment ought to be in pos- session of the general bearing and undulations of their respective metalliferous channels, without which the work must be attended with great risks: guess work, “where it is there it is,” 1s an ex- tremely bad principle to go by, even with a good practical miner ; but when exposed to the changes of agents, inexperience, &c., the consequence may be easily conceived. After great expense has been incurred in carrying on works through unpreductive rocks, mines have frequently been abandoned, when within a few feet of rewarding our search, for the want of knowing the width and positions of the barren and rich channels of ground. On the other hand, in prosecuting works of discovery in a direction where no metalliferous channels exist, mines have been carried on at a considerable loss, simply because the vein happens to be in the same direction as another more productive. Of all speculative employments, mining has been, and continues to be, for the want of a well-founded principle, the most uncertain ; ex- perience and ingenuity being frequently and completely defeated, although the miner has been continually led to suppose himself on the point of meeting a good course of ore; while from veins, 53 which men of equal ability have abandoned, large profits have afterwards been realized. Therefore the theory of the formation of mineral veins, and the rules which lead to the discovery of the richer deposits, are objects of much greater national importance than is generally supposed. It is essential to the interest of every mining proprietor to know the general character of the local dissemination of the minerals in the district, and indispen- sable to his forming a correct judgement on the mode of work- ing adopted by the practical miner. The metalliferous deposits are subject to be decomposed and recompounded periodically, according to the nature of the local changes. In some situations it is possible that veins may change their character in a comparatively short period, so as to be rich at one time and poor at another, especially if kept full of water. Numerous instances may be mentioned where old workings have been partially filled with a fresh crop of minerals, and also where minerals have been decomposed and disappeared. After the production of some crystals these are again decomposed by new elements ; and thus we find crystals have disappeared after having once served as nuclei for others to be deposited upon. A kind of efflorescence of gold, blende and pyrites have been found formed on the walls in old workings in the mines of Mar- mato in New Grenada. Gold washings are often abandoned, and the very same sand becomes again sufficiently rich to be re- washed, if situated immediately on a primary rock. Capillary gold, silver and copper have been found formed in old workings near Ibague, subsequently to the mines having been worked by the Aborigines. Native copper has been found formed on the timber in the Wicklow mines. Mr. W. Forster states, that at Wolfclough mine, in the county of Durham, which was closed for more than twenty years, and opened again, needles of white lead ore were observed projecting from the sides of the veins, more than two inches in length, being equal to a vein two inches wide. D’Aubuisson observes, that in the mines near Pontgibaud, fer- ruginous and calcareous deposits are now effected in the open spaces left in the mines; so that if after working out the lode the galleries be left shut, and filled with the solutions of the bounding rocks during a long series of years, new workings 54 could be carried on upon the new deposits.. The rubbish left in old workings becomes often cemented by mineral salts, which sometimes crystallize in the crevices, so as to render it worth working over again in the course of a very few years. In the mines of Hanover a leather thong suspended from the roof of a mine was found coated with silver ore, and also native silver and vitreous ore coating the wooden supports of a mine which had been under water for several years. These chemical actions, governed by the subterranean polar currents, continue to fill every fissure or vacuity with crystals, the growth of which swells open the cracks, and thus causes new fractures and dislocations, according, to the variable nature of the containing rocks, and the amount of resistance. This gra- dual opening of the veins with the growth of the crystals from the sides accounts for the isolated masses of the bounding rocks found in veins (Plate XIII.), which could not possibly occur had they been open fractures. Indeed the hypotheses supposing mineral veins to have been filled by solution from above, or that of the injection of igneous matter into an open fissure from below, are so crude and irreconcilable with the nature of their contents that they do not deserve our attention: the facts brought for- ward fully justify the conclusion that a// veins, whether they be mineral or not, have been formed and filled on the same prin- ciple of polar action as above described. In the east and west, or transverse fissures, the crystals are formed from side to side, and in the splits, longitudinally, in parallel plates, as shown in Plate X. The bunches of mineral in the splits are in diagonal and longitudinal shoots. (Plate XV.) Roots and Branches of Mineral Veins. The meeting of a number of small veins either in depth or in a horizontal direction is favourable for the accumulation of mi- nerals. Plate XVIII. represents a plan of a split vein in New Grenada containing silver ores; the feeders or roots, and the northern branches, are laid down according to the manner in which the mineral concentrated and dispersed northward. Many are called feeders by miners which in reality have had the con- trary effect. The feeders of the east and west veins, like those of the splits, 55 are on the south side; the branches seen on the opposite side have, generally speaking, allowed the mineral to escape from the veins. An oblique fissure on the south side, called a caunter, formed contemporaneously with an east and west vein, produces the same effect as the small oblique branches, viz. enriching one part of the east and west fracture at the expense of another : the lode north of the oblique vein would be found comparatively poor. These facts may be observed in Cornwall in various parts, and particularly in the mines of Dolcoath, Tin Croft, and North Roskear. The feeders or roots of the split veins may be seen in the mines of St. Just, the bunches of mineral depending entirely upon them ; the principal being those coming in from the granite in a8.S.E. direction, and forming diagonal shoots of ore from their junction northward, as represented in Plate XV. The tin ore formation in the St. Ives consols may be described as a number of large roots coming in from the south-east, con- verging into one grand trunk, and growing northward at an angle of about eight degrees from the horizon, surrounded by the granite. A similar split vein may be also seen on the banks of the Tamar, having the principal feeding veins or roots on the south-east side, in tender ground under the bed of the river. Split veins, cross courses, &c. are not productive without the feeders, the latter being the only means by which the contents of the bordering rocks can be brought into them. The split veins of all mining districts are of the same nature ; _ therefore as these effects are matters of fact, and easily referred to, we shall not enter into further details. All split veins, be they quartz, carbonate of lime, hornblende, or any other, have been formed in the same manner, and consequently the contents are arranged in longitudinal plates. The influence of the impermeable Splits on the accumulation of the Minerals in the Transverse Fractures. Independent of the “ bunches” of mineral being found cor- responding to certain channels, the amount of the deposits in the fissures is considerably influenced according to the position of the intersecting splits. (Plate X VII.) 56 That veins of fractures are enriched near their intersection by cross-courses, fluccans, faults, &c., is a fact well known in Corn- wall, North Wales, and the North of England; the same fact is also observed in Germany, in Mexico and South America: the evidence for which is very clear, inasmuch as the bunches of mineral are sometimes found confined to one side of the splits, as represented in the Plate. This well-known fact is another proof of the east and west fractures having been filled subse- quently to, or contemporaneously with, the formation of the splits. These accumulations of minerals appear to have been pro- duced by the splits having been filled with substances imper-- vious to water, the metallic solutions being thus retained entirely — on their respective sides; and when one side happens to be more strongly impregnated than the other, the quantity of minerals formed in the transverse fissures will be found in the same re- lative proportion. The sketches in Plate XVII., illustrating these kind of accumulations, have been taken from mines in America and Europe; therefore they may be considered as real sections, to which we beg reference for a more clear idea of this interesting part of our inquiry. The impermeable porphyritic channels have the same influence on the deposits of minerals as the cross-courses, or meridional splits, 7. e. they dam up and retain the metalliferous solutions on one side, and thus produce large accumulations. In South Roskear, Tin Croft, and some other mines in Cornwall, the mi- neral is found almost entirely confined to one side of their in- tersecting cross-courses and hornblende veins. One of the most noted examples of this fact, mentioned in the Geological Report of Cornwall, is that of Wheal Alfred, near Guinear. The elvan vein, Plate XVII. fig. 1, runs from south-west to north- east; the lode intersects it obliquely ; while in the slate, on the eastern side, it contained mineral ; but on approaching the elvan it became much richer, and yielded sufficient ore to afford a profit of £140,000. After quitting the elvan on the western side the jude became poor, and eventually the mine was abandoned as unproductive. The arrows in the sketch represent the nature of the accumulation on one side of the elvan, and the apparent cause of the poverty on the other. Viewing the subject on a 57 large scale, the accumulations produced by impermeable veins will be found according to the following order :— When the splits or veins run from south-west to north-east the “ bunches ” will be found principally on the eastern side; if the splits run from south-east to north-west the deposits will be found on the western side, being the natural consequences of the oblique mechanical interruptions of the solvents transmitted through the grain of the rocks by means of the magnetic currents. Nume- rous minor variations must necessarily occur from the effects of local causes ; but we need not describe them, as we hope that the principle here laid down will be found sufficient for the guidance of the practical miner. Recapitulation. In the preceding observations we have endeavoured to reduce to order and system those vague indications applied by miners to guide them in their subterranean operations, and concentrate those scattered rays of information which have been obtained by long experience, but have been hitherto so much diffused as to lose their value. First. We have shown that the cleavage planes are not mere local phenomena, but an universal structure—a polar grain, formed uniformly more or less vertically from pole to pole, caused by a subterranean molecular action, or the circulation of the magnetic currents from south to north. Secondly. That the crystallization and meridional structure of the primary base, from aqueous solutions of the elementary sub- stances, have been, and continue to be, formed by the constant action of the currents of terrestrial magnetism from south to north. Thirdly. The order of the splits, and transverse fractures in the crystalline crust of the earth, is caused by the magnetic ten- sion ; with the progressive opening and filling of the ruptures by the moving solvents in the intersecting rocks, according to the nature of their respective contents. Fourthly. We have also exhibited the order of the disloca- tions, or “ heaves,” and the influence of the impermeable splits on the contents of the fractures. The more closely and minute the investigation is made, the more convincing is the result; 58 therefore this general principle may be safely applied to any mining district, be it in America or Europe, and it is so simple that it requires no other aid than the magnetic needle, the know- ledge of the local grain or lamine of the district, its metalliferous channels and configuration, to enable a person to know where the minerals have been principally deposited, and where scarcity of minerals prevails. This principle, that is, the laws of ter- restrial magnetism, is therefore obviously of vast importance to the practical miner, and the elucidation of the subject to the fur- thest practical extent is the greatest desideratum which now re- mains in the art of mining, since the operations carried on for the discovery of the deposits of ore contained in mineral veins, not only constitute one of the heaviest expenses of mines, but it is the vague and precarious result of these trials which chiefly stamps the proverbial character of hazard and uncertainty which is attached to the pursuit. We therefore trust that the above outline will tend to simplify this interesting subject, and remove that embarrassment and complexity which have hitherto im- peded the progress of this department of geological science. CHAPTER IX. QUICKSILVER DEPOSITS. In the mines of Bavaria this metal exists in a variegated sand- stone resting on slate. It occurs in transverse fractures inter- secting meridional channels of ground, which are nearly perpen- dicular. The ores of Cinnabar in the mines of Idria are inclosed in friable talcose rock, interlaminating in small veins in meridional channels. In Peru the quicksilver is found like the silver ore, principally in the lamine of the meridional channels. It will therefore be observed that ail metals are similarly transmitted or deposited in rocks. 59 Saliferous Deposits. No satisfactory hypothesis has yet been advanced to account for the occurrence of rock-salt (muriate of soda)*. Some have endeavoured to maintain that it was deposited by the ocean like the sedimentary rocks. The strata above the salt contains organic remains, as do also those below, but the salt contains none. The entire absence of marine exuviz from the strata of salt shows that such rocks could not have been deposited in the sea; and it would be difficult to conceive how such avery soluble substance could crystallize in a large body of water like the sea. Others think that it was produced by heat. Not only are salt rocks always found impregnated with water, but they sometimes inclose sub- stances incompatible with the action of heat. Crystals of salts can only be produced from aqueous solvents, and although heat is employed to expedite the process in arti- ficial works, it is not essential for the formation of the crystals, as a crystalline mass formed from solution is effected by polar action alone at common temperature. When salts are crystal- lized, they frequently retain a portion of the solvent not me- chanically mixed with them, but as an essential component, to which their regularity of figure and colour is in some instances referrible. Thus Glauber’s salt contains a great quantity of water, and crystallizes in six-sided prisms, transparent and beau- tiful; expose them to heat, the water of crystallization flies off, the crystals lose their shape, and crumble down into white powder. Crystals of gypsum are of glossy transparency, and of regular figure; this is due to water: heat them, they crumble into a white powder, well known as plaster of Paris. Such is the aqueous nature of all natural crystals as well as salts ; hence we have abundant reason for assuming that crystalline masses have been gradually formed out of aqueous solutions of the substances permeating the rocks. It was once supposed that the deposit of salt, or muriate of soda, was confined to a particular series in the order of the se- dimentary rocks ; but the fact is, that salt springs are found to * Salt, in the common acceptation of the word, implies culinary salt ; but it denotes a variety of substances, totally distinct from common salt. Thus marble is a salt ; so is pearlash, blue vitriol and plaster of Paris. 60 issue out from all kinds of formations, from the granite upwards, in different parts of the world, and become gradually crystal- lized and consolidated in any rock which may be of a loose and porous nature, and not heavily pressed. The deposits of rock-salt and the springs of muriate of soda in the eastern Cordillera, suc- ceed each other from Pinceima on the south to the Llanos de Meta on the north, a distance of about 200 miles in the same linear direction. All the known salt springs in South America are found in bands more or less meridional. When the salt does not form beds it is found interwoven in clay, that is, in small veins, like white carbonate of lime veins in a black limestone. The fibres of salt are found perpendicular to the sides of the cracks, like the quartz in veins of fractures. In the splits and horizontal seams the salt is generally divided into thin parallel plates, varied in colour, siuous, and similar to the general appearance of quartz and other substances in meridional and horizontal veins. Salt springs issue from the micaceous schist on the western side of the plains of Mariquita, from the porphyry of the west- ern Cordillera near Supia, and apparently from the fissures in the granite in Autioquia. Near Lima, rock-salt is pierced through by veins of porphyry. ‘The direction of the subterranean salt springs, like that of all mineral solutions, is independent of the inequalities of the surface, and may be traced for miles in me- ridional bands. In England we find the saline springs similarly situated. We may consider Dudley, in Worcestershire, as the northern part, and the mineral waters of Cheltenham as the southern ; all the brine springs are situated in the intermediate space, and almost in a north and south direction. Hence we have only to apply the polar force, in connexion with solutions, to account for the formation of salt like all other subterranean products. The natural process is constantly going on under ground without the aid of heat, at least in the sense in which this much-abused chemical phenomenon is employed in geological theories. ; What we have stated above respecting the formation of salts from saline solutions, and the gradual formation of veins and horizontal masses by the hydrostatic power of the solutions, and the force of the crystallizing power of the substances, equally 61 applies to veins called dykes, hornblendic seams interstratitied in sedimentary beds ; such as the Whin sill of the North of En- gland, veins of carbonate of lime, &c., that is, they are forced into the joints in an aqueous state subsequently to the formation of the inclosing beds. A very interesting article on this subject appeared in the Mining Journal, which appears to have been written by a prac- tical person who had examined such a formation near Wolver- hampton : the following is an extract:— Some geologists not only maintain that the trap rocks which are interstratified amongst the beds of the carboniferous rocks of England were forced into their present positions in an igneous state, but they also point out the centres of eruption from which they were injected into the coal measures. Several such centres of eruption had been long pointed out in the Wolverhampton district; but, like numbers of other questionable points on this subject, persons seldom take the trouble of contradicting them, by giving a bond fide representation of the facts, to check the progress of such igneous absurdities. “The occurrence of the large masses of green rock, called ‘trap, at Pouk Hill, the Nechells, and other localities in the Wolverhampton district, is not owing to these points being cen- tres of eruption, but simply to the bed of greenstone (which is hornblendic) throwing off branches from its upper surface, which branches in parts are exposed on the surface; the under part of the above bed of trap maintaining its position unchanged, and the coal measures ranging underneath it, in a comparatively un- disturbed state, as observed in the workings below, showing very clear that the disturbance in the district is confined to the upper part of the series, and proceeding solely from the action of the bed alone upwards, and not from an igneous intrusion from below. ‘This trap, or hornblendic bed, is always moist, and in parts as soft as clay; and when this happens to be the case, the dis- turbance appears to be greatest, and the beds in contact are often seen fractured, and saturated with mineral water, and the cracks filled with calcareous and siliceous spar proceeding from the large bed of trap,—and, as the upper beds present the least resistance to the swelling or apparent increasing power of this reck, the fractures and veins are formed upwards, and bear the same 62 analogy or relation to it as the larger masses do, and similar to the veins usually observed in slate-works when resting on granite. These branches appear as if they had been squeezed or forced up from the trap bed by the pressure of the superincumbent beds upon it, similar to what would take place in a bed of soft clay confined, if covered by a layer of stones; the clay would be forced up between the joints, and such are what are called centres of eruption in the above coal district. Where the coal happens to be in contact with the above rock, it is more or less impregnated with substances corresponding to it, and always saturated with mineral waters, which coal, when dry, presents a somewhat reddish and greyish appearance, vulgarly called ‘ burnt coal;? but absolute fusion had no more to do with this change in the character of the coal in contact than it has to do with any other slow chemical saturation by the humid way. “The following quotation from a recent work on this subject will give some idea how the volcanic action is pushed beyond its natural limits to explain phenomena with which it either has none, or, at best, very little connexion; and it will also exhibit the kind of reasoning, called ‘a strict process of induction,’ by which the igneous theory is established :-—‘ The modes in which trap rocks, and, in fact, all the primary rocks occur, strongly countenance the idea of injection from below; and their occa- sional striking resemblance to the products of existing volcanoes shows that the agency by which they were produced was that of subterraneous heat, and therefore closely resembling, if not identical with, volcanic action. One or two decisive facts in support of these views may not be misplaced. When dykes or masses of basalt or trap come in contact with beds of coal, the coal in its vicinity is generally found to be converted into coke or cinder, clearly proving, that when the basalt assumed its pre- sent position, it must have been in an intensely heated state; and as it now occurs, completely filling the cracks, &c., im the coal strata, there can be no doubt that when ejected from below it was in a state of actual fusion. Were further proof needed that such is the origin of basalt or trap rocks, it would be fur- nished by the fact, that this rock often resembles lavas, not merely in its external texture, but in actual composition. We have thus clearly established the igneous origin of this class of 63 rocks ; and it is sufficient to observe, that by equally satisfactory, though, perhaps, less self-evident reasoning, the same origin may be ascribed to all the rest. In this manner it will be seen that by a strict process of inductive reasoning, we are enabled to arrive at conclusions no less interesting than important with re- gard to the nature of those powerful agents,’ &c. &c. “‘ Such are the reasonings by which it has been concluded that the above rocks are of an igneous origin, which, forsooth, is called a strict process of induction! Fortunately for our underground operations, our practical men laugh at such absurdities, and are guided by better reasoning, founded on daily experience ; but it is on young men, such as surveyors, &c., who have been taught such doctrines in the academies, and are too often placed in re- sponsible posts, where such ideas lead to bad results, and who are under the impression that every vein or rock of what they call trap is the relic of a former volcano,” &c. &c. One of the most usual effects of heat upon limestone is to de- prive it of its carbonic acid and reduce it into a white powder. We know of no instance of lime having been reconverted into a crystalline limestone by heat. Chalk, when intersected by veins of any substance containing carbonic acid, is partially converted into marble by the impregnation or absorption of the acid from the veins. One of the most direct objections to the supposed igne- ous rocks was first drawn from the appearances of the calcareous strata in contact with basalt; but the assumed igneous element, with its effects, appears by its supporters to possess extraordi- nary properties,—remaining unaffected im water as well as in the air, hot or cold, according to circumstances; capable of convert- ing limestone into lime, or lime into limestone, as they may feel disposed to apply it, and totally uncontrolled by any fixed principle or the known laws of heat. Much has been written against the theoretical deductions of Werner; but however in- consistent they were, those which have been founded on the assumed igneous agency are much more arbitrarily drawn, most irregularly applied, and totally irreconcilable with the observed phenomena, and have tended quite as much as the dogmas of our predecessors to bring the geological science into disre- pute. Those who feel an interest in this subject, i.e. the contact of hornblende veins with limestone, coal, &e., may examine the 64 dykes in Anglesea, Newcastle, and Durham; they afford abun- dant evidence of their aqueous nature and growth from a semi- fluid base, and the effects at the points of contact are such as would naturally take place by dissimilar substances in a moist state, subject to a slow chemical action. CHAPTER X. POLARITY OF EARTHQUAKES. Ir any persons should be more in favour of the igneous theory than others, it might be supposed that they would be those accustomed to earthquakes and volcanic actions; however, nine years’ residence on the Andes has produced on the writer, as will be observed, the very contrary impression. As we have already stated, one striking peculiarity in the American earth- quakes is their meridional action from south to north. The shock of the earthquake of Chili in 1822 was felt simultaneously throughout a space of 1200 miles, from south to north; the la- teral oscillations being confined to narrow bands. The following are a few registered by the author :-— 1834. Jan. 20.—Violent shock from Chili to St. Martha in a more or less meridional direction; caused great damage in the line of its maximum force. Its meridional dis- turbances were felt over a space of 1500 miles of linear measurement; but the transverse oscillations scarcely extended over 200 miles on land. 1835. Feb. 20.—Ditto, a great number, and continued more or less daily until the month of March. 1836. Jan. 4.—Slight shock from the south. Jan. 8.—Ditto. 3 On the central Cordillera, from four to five shocks al- most daily, from the 1st to the 15th. 1837. Nov. 10.—A shock from the S.S.W., accompanied by sub- terranean thunder, after heavy rains. Nov. 27.— Ditto, after a few days intense heat. 1838. June 19.—Two violent shocks; no oscillations; the ground appeared to heave up. | 1838. 1839. 1840. 1841. 65 Aug. 9.—Sounds heard in the mines, passing in the direc- tion of the cleavage from south to north; no oscilla- tions; the magnetic needle much affected. Aug. 11.—Shock accompanied by a very loud explosion, apparently from the volcanic vent of the Paramo de Ruez. May 28.—A severe shock, continued for nearly a minute. Sept. 21.—Ditto. Sept. 22.—Ditto. Sept. 28.— Ditto. All in the usual direction, from south to north. Oct. 15.—A great number of shocks during the last few days. The quantity of rain fallen last month exceeds that of any month in the last three years, viz. 153 inches. Natives consider earthquakes to follow the extremes of wet or hot weather. Nov. 28.—Ditto. Dec. 13.—Three very violent shocks from the 8.S8.W. to N.N.E. Jan. 2.—Strong shocks from the south. June 12.—Ditto, the oscillations confined to very narrow limits. Aug. 22.—A sharp shock from the south. Dec. 11.—A severe shock from the south, lasted fifty seconds; several houses thrown down in Antioquia in its line of bearing. Mar. 12.—Slight shocks from the usual direction. Mar. 19.—Ditto. June 1.—Ditto; the magnetic needle much affected. Sept. 8.—A severe shock. Sept. 14.—A slight shock. Sept. 30.—Ditto. The whole of the above, without exception, were from south to north, and oscillating from east to west. It will therefore be observed that earthquakes are subject to laws of action as uni- form as other natural phenomena. In 1797, the district around the volcano of Tunguraqua in Quito, during one of the great meridional shocks, experienced an undulating movement which lasted four minutes. At the FE 66 foot of the Paramo the earth was rent open, and streams of water and foetid mud with fish poured out, overflowing and wasting everything. During several of the eruptions which have taken place since the year 1822, on the western coast of Chili, some were seen which were followed by great whirlpools, as if the sea was pouring into cavities of the earth. The volcanoes of Ni- caragua, in Guatimala, during their activity, are commonly at- tended by whirlpools. Had there been such an igneous nucleus as the one assumed by the plutonists, covered only by a thin crust, what would be the consequence when the sea happens to pour into it? There would certainly follow some awful cata- strophe; but we are happy to state no such convulsions have occurred. Aqueous products and muddy matter are more com- mon than lava or melted rocks; and we find that they generally contain putrid fish of the adjoining sea or lakes, as the case may be. Hence, if we take the products, their effects, and linear ac- tions into consideration, we have strong evidences in favour of considering the whole phenomena due to electro-magnetic action. CHAPTER XI. THE NORTHWARD AND UNDULATING MOVEMENT OF THE EARTH’S SURFACE EN MASSE, BY THE CONSTANT CIRCU- LATING ACTION OF THE MAGNETIC CURRENTS. F Roo the apparent quiet and regular succession of natural events to which we are accustomed, and the repugnance we feel to the idea that it is possible for the common course of nature to change the general appearance of the surface without causing interrup- tions, we might, without due investigation, almost persuade our- selves that the physical features and conditions of the globe pos- sess an unchangeable character. Indeed the general phenomena of nature which are daily before our eyes, are often those which are considered the least attentively. In looking at an extensive forest for a hundred years, it would appear to a superficial ob- server that he was viewing the same identical substances all the time, yet there is no truth more certain than that the whole, or 67 nearly so, would entirely change in the interim. Continents are changing their physical aspects and configurations—emerged and submerged from the level of the ocean, and moving in masses, unobserved by the millions of animated beings who have their existence on them. Generation after generation disappears while others are taking their places, and so gradually and imperceptibly are these effected, that without reflecting a little, and comparing the past with the present, we almost look at things as if they had been always in the same state. So familiar and reconciled we become to the altered condition, that the past is soon forgotten, and man, who is linked to these renovating laws of nature, too often forgets his final destiny. That the dry land does not possess that fixity of position, or that it is not a solid and immovable mass attached to a solid globe, as formerly supposed, is now well known; and the earth- quakes of South America abundantly testify that the surface is a flexible crystalline compound floating on some more dense fluid, and subject to perpetual movements. There have been very opposite opinions entertained respecting the effects of the earth- quakes on the coast of Chili. Some maintain that the coast was permanently raised at various points during the earthquakes of 1822-34-35, &c.; others oppose such statements by very circumstantial evidence; yet both parties agree that the coast is at present at a higher relative position at various points than it was formerly. That such a disparity should occur in observa- tions made by parties who were living on the spot is somewhat singular, and shows how cautious we should be in drawing con- clusions on observations made by a hasty survey. The cause cf the above conflicting opinions is simply this: the whole western coast is gradually rising, from Terra del Fuego to central America, and so insensible is the action that it is effected unobserved, until an earthquake draws attention to the changes, when the whole is immediately attributed to that phenomenon by those who may not have attended to the exact height of the sea previous to the shock. That the earthquakes do occasionally cause undula- tions in the coast there can be no doubt, but they are compara- tively insignificant to the great changes effected by the silent operations of nature. The electro-magnetic tension is sometimes so great in the Chilian range as to cause immense transverse F 2 68 fractures and meridional splits, from which water is sometimes seen bursting out. With regard to lands being gradually elevated and depressed unaccompanied by earthquakes, Professor Lyell has abundantly proved in his ‘ Principles of Geology,’ and has also made very lucid observations on this part of our subject. The coast of Brazil is subject to changes like the Chilian coast, although earthquakes are seldom felt there; but we have more satisfac- tory proofs in the gradual sinking of the western coast of Green- land, and the equally slow and gradual movement taking place throughout a large part of Sweden and Finland, and a number of other parts in the northern hemisphere, where earthquakes are seldom felt. How much more satisfactory and consistent with the ordinary laws of nature is it to regard these grand opera- tions as regular and necessary effects of great and general causes of the action of terrestrial magnetism, than to suppose them as resulting from series of convulsions and catastrophes, regulated by no laws, and reducible to no fixed principles ! In making comparisons between the ancient latitudes of twelve places in South America with recent observations, we find an average difference amounting to about twenty minutes in favour of a more northerly position. Humboldt took the latitude of Mariquita about forty years ago, and made it 5° 13! O” north. The author continued a series of observations in the same neigh- bourhood, and connected the above point with others by trigo- nometrical measurements: the latitude of the same spot is now 5° 25! 30". The observations were not confined to a star or the sun alone, but taken from various celestial points, with their complementary angles, by fixed theodolites, a sextant, and a re- peating circle. Similar observations were made at other points. It is therefore concluded that South America is not only subject to vertical undulations, but also to a horizontal movement en masse northwerd, amounting to at least ten seconds per annum. However, we shall not dwell on this fact, but shall refer to other evidences, as being more substantial and satisfactory proofs of the northerly movement of the earth’s surface. It is the neces- sary consequence of the action of the polar force, which may be proved by an artificial globe having an electro-magnetic axis, placed horizontally in a fluid containing salts: the masses formed _= 69 at the negative pole will be found propelled as they are formed toward the opposite pole. Granting these mutations in the southern hemisphere, it may be said that they cannot have been going on during the last thousand years in the northern hemisphere, otherwise they would have been detected by astronomers, as the latitudes of places must have varied. - | Let us examine what were the actual appearances of the is- lands and continents, with their respective positions in the time of Ptolemy. In comparing Ptolemy’s observations with the present we recognize great discordance. Even at the beginning of the last century the position of places could not be depended upon within 20 minutes. Jet us suppose that the position of a place was known a hundred years ago, and that it was situated exactly in the equator; in comparing the same point at distant intervals of time with the same celestial objects, we find a dif- ference amounting toa measurable quantity; and this difference is proved by astronomical observations to be in one direction. Consequently, in order to denote the latitude, or rather to pre- serve it in the same relative spot, the position of the celestial objects must be altered. This change is called the precession of the equinoxes. ‘To account for this movement it has been as- sumed that the axis of the globe is continually altering its rela- tive angular position in space, which apparent movement during the historic period has been northward. The amount of this motion, by which the equinox appears to travel, is 50 seconds per annum, producing a change along the meridian of about nineteen seconds. ‘This relative change destroys, in the lapse of _a moderate number of years, the arrangement of the catalogues of stars, and makes it necessary to reconstruct them. Since the formation of the earliest catalogues on record the place of the equinox has retrograded about 30 degrees. : When the above hypothesis of the precession was propounded, the earth’s surface was considered as a fixed and immoveable mass. So little was known of the phenomena of geology, mag- netism, &c., that they were not consulted; hence a change of the whole globe appeared necessary to account for the observed variation. The cause of such a movement has been attempted to be explained by the assumed geometrical forces. It would be 70 easy to analyse the hypothesis, but as we have questioned the very foundation of the principle on which it is founded, we need not dwell on it here, but simply state, that the movement of the surface of the globe northward accounts for the above effect in a more convincing manner, and more free from intricate computations, than the geometrical physics now used in astro- nomy. Besides, the supporters of the theory leave a residual phenomenon equal to about ten seconds unaccounted for, and an- other movement in the ecliptic ; hence we have abundant proofs by celestial observations of terrestrial changes in a northerly direction. It may be argued, that if the masses of dry land, which are now situated near the north pole, containing organic remains belonging to the tropics, have been propelled there by such a slow northward action, it must take some thousands of years since they were in the torrid zone more than we admit according to our chronology, supposing the relics are the re- mains of those given to man. There is no proof that they are not the relics of those given to man, and we have abundant evidence of the fossils of the existing organic beings being found with those which have become extinct; therefore no line of separation can be legitimately drawn between them. With re- spect to our chronology, it is not well defined, 7. e. not a demon- strable quantity; it is a mean of a compound composed of un- certain quantities, therefore necessarily an uncertain amount. Not one of the chronological records was considered sufficiently certain to be adopted—-the Egyptian and Chinese were left out —therefore it is useless to enter into this question; besides, it matters not to our creed whether the globe was created 7000 years or 30,000 years ago; time cannot make any difference in a faith which is founded on too firm a foundation to be shaken. Plato says that the world changes its superficies in every re- spect; that the heavens and the stars appear to change and reverse their movement by time, in such way as that the east appears to become the west; we find also the Egyptian priests acquainting Herodotus, that from the commencement of the dynasty of their kings (which according to their computation extended to more than 11,000 years) the sun had apparently changed his course in the heavens four times. We can easily conceive that a country like Australia, which is 71 now south of the tropics, if brought-up to the northern hemi- sphere, would cause the sun to appear to rise on the left instead of, as in the former situation, on the right: probably such effect was the origin of the above notion of the Egyptian priests. The observations of the ancient philosophers have been lost in the lapse of ages; however, we have great advantages in our present investigations; the records of the past have been laid down and preserved by a power beyond the reach of human control: we may recall the past and anticipate the future by means quite independent of the conflicting and imperfect evi- dences of human record. With regard to the actual time since the creation of the sy- stem, it is a question so totally beyond our reach, that it is as useless as it is unreasonable for us as finite beings to enter upon the subject; all that we can legitimately speculate upon is the nature of the dry crust we call land. The comparatively recent origin of the existing organized beings appears abundantly evi- dent, and there is a still more decided proof that the whole of the present dry land as it becomes oxidated at the north pole, will come to an end; and unless a corresponding dry land con- tinue to rise from the southern hemisphere, towards which the living system may retrograde, the world must come to an end, independent of the existence of the globe itself as a body in space. There are many philosophers who admit in its full extent the doctrine of final causes as evinced in the structure of a plant or an animal; or, in other words, who readily grant that all the various parts and organs conduce to one definite purpose; yet they are reluctant to allow that the earth itselfis under any other guidance than an irregular and confused igneous element. We have no reason to suppose that the laws which govern the whole body of our planet are not directed by the same wisdom as that displayed in the external world. Every part of the surface of the globe is adapted to the wants of man, and the inferior cre- ation by which he is surrounded; it is not the result of chance, or of any imaginable fortuitous circumstances, but the produc- tion of a season,—it has 1 its beginning and ending, like animated nature. 12 CHAPTER XII. THE NORTHWARD MOVEMENT OF THE SURFACE PROVED BY THE CLIMATE OF THE LAND IN THE NORTHERN HEMI- SPHERE GETTING COLDER. WE have evidences of the northern movement of the surface in the changes of the temperature of the northern hemisphere. Within the limits of the historic records we have abundant proofs of the climate of Europe getting gradually colder, and that the inhabitants of the north are continually retrograding southward. The first settlers in Iceland found extensive dis- tricts of that now dreary country covered with forests of birch and fir. They were also able to cultivate barley and other grain. At present the whole island is a naked desert, the native woods have totally disappeared, and the Icelanders have long since relinquished, for good reasons, the practice of growing corn. The relics of the past in this island are few, but sufficient to prove its former habitable state. One of the most remarkable circumstances attending the discovery of Iceland is, that relics were found there which showed that it had been previously in- habited. ‘The nature of these relics, which consisted of bells, wooden crosses, and books in the Irish character, induced the Norwegians to believe that those prior inhabitants were Chris- tians either from Scotland or from Ireland. The most ancient of the Icelandic chronicles are not con- tented with mentioning the vestiges of former inhabitants, they distinctly state that there were actual settlements on the island previous to the Norwegian emigration *. They name Kirkinbui, one of the warm and fertile valleys that occur on the southern coast, as the residence of those pape, as they called strangers, who deserted the island, it is added, from their aversion to the pagan colonists. Greenland, according to most of the Icelandic histories, was — discovered in 982, and peopled four years later. But there * Lardner’s Cyclopedia, Maritime Discovery, vol. i. p. 216. 73 exist letters patent of Louis the Debonaire in 834, and a bull of Gregory IV. in 835, which confers on the church of Ham- burg, among other privileges, that of converting the heathen in Iceland and in Greenland. The new settlers in Greenland had their bishops from Eu- rope, and continued their intercourse with the parent state of Norway till the year 1418. The colony paid to the pope an annual tribute of 2600 pounds weight of walrus’ teeth, as tithe and Peter’s pence. The dreadful pestilence, called the black death, which in the middle of the fourteenth century depopu- lated all Europe, extended its ravages to Greenland. The colony was, from this and the increased severity of the climate, en- feebled, and soon after disappeared from history. There was a country called Vinland within a few days’ sail of Greenland, watered with rivers yielding abundance of fine salmon, on the banks of which were trees loaded with agreeable fruits, the temperature delicious, and the soil very fertile. Amongst the fruits were found grapes, which was the cause of their naming it the land of wine. It is impossible to shake the authenticity of the above circum- stantial accounts of the Northmen; and it is likewise difficult to acknowledge their genuine character without admitting at the same time that Vinland was in Newfoundland. Wine was made from grapes which grew formerly in the open fields of England and the north of France, and there are ample proofs of a similar reduction of mean temperature in other parts of the continents of Europe andin North America. It is in the northern regions that we find relics of man and his works, and probably the greater part have disappeared, owing to the rapid destruction and oxidation of the land at this pole. According to a recent account, several subterranean stone laby- rinths have been discovered in Lapland, Nova Zembla, and some of the islands lying near the coasts of Finland, particularly in Wiez, which is all desert, called by the natives Babylons*. Arabian coins are found in many parts of Russia, along the Volga, and northward even as far as the White Sea, all of which are of a date anterior to 10107. * Athenzum, part 190. + Lardner’s Cyclopedia, Maritime Discovery, vol. i. p. 169. 74 When we descend below the surface and examine the remains of the organic system now inclosed in the rocks, the proofs of the change of climate is much more decisive, and free from all the doubts arising from imperfect history. So striking has been the general northward action on the surface, that such effects have been long observed. Kirwan stated, that in the northern latitudes beyond 55° we find the animal spoils of the southern countries and the marine exuvie of the southern seas; but in the southern latitudes we find no remains of animals, vegetables, or shells belonging to the northern, but those only belonging to the neighbouring seas. Subsequent surveys have proved the above remark to be a fact. It is now fully admitted that the sedimentary rocks of the northern hemisphere were, at a former period, or during their deposition, exposed to a much hotter climate than they are at present. In the superficial de- posits of sand, gravel and loam, strewed over all parts of Europe, remains of Mammalia are discovered, among which are those of — the elephant, rhinoceros, hippopotamus, bear, hyzena, lion, tiger, crocodiles, and others, consisting of genera now confined to the tropics. Professor Lindley justly remarks, that it is an important fact, “that at the period of the deposit of the Lias the vegetation was similar to that of the southern hemisphere, not alone in the simple fact of the presence of Cycadez, but that the pines were also of the nature of species now found only to the south of the equator. Of the four recent species of Araucaria at present known, one is found on the east coast of New Holland, another in Norfolk Island, a third in Brazil, and the fourth in Chili*.” “With regard to the degree of analogy which the productions of different regions may be found to present,” says Professor Phillips, “ with the fossil reliquize of the lower series of rocks, we are not aware that any investigations are on record; and yet itis impossible to — turn to Australia without a suspicion that the productions of that region have more than the average resemblance to the primzeval fauna and flora now found entombed” in the northern hemi- sphere. In the coal deposits the proofs are equally striking that they were deposited in a climate like the southern hemisphere, * Foss. Flora, vol. xi. p. 21. gs and that no coal except a recent formation of lignite is found from the tropics southward ; in a word, the whole of the deposits of the southern hemisphere are comparatively recent, whereas those of the northern are more or less ancient. “Tt is not merely by reasoning from analogy that we are led to infer a diminution of temperature in the climate of the lands now situated in the northern hemisphere; there are direct proofs in confirmation of the same doctrine,” says Professor Lyell, “in the only countries hitherto investigated by expert geologists where we could meet with such proofs. It is not in England or Northern France, but around the borders of the Mediterranean, from the South of Spain to Calabria, and in the islands of the Mediterranean, that we must look for conclusive evidence on this question; for it is not in strata where the organic remains belong to extinct species, but where living species abound in a fossil state, that a theory of climate can be subjected to the experimentum crucis. The fossils of the Subapennine hills, and their living analogues from the tropics, correspond in size; but the individuals of the same species from the Mediterranean are dwarfish, and appear degenerate and stunted in their growth, for want of conditions which the Indian Ocean still supplies. This evidence is not neutralized by any facts of a conflicting character; such, for instance, as the association, in the same group, of individuals referrible to species now confined to the arctic regions. Whenever any of the fossil shells are identified with living species at or near the equator, it is not in the North- ern Ocean, but in the Southern that they must be sought.” When geologists assumed an igneous globe undergoing refri- geration, to account for the former high temperature of the northern hemisphere, they imagined that the southern hemi- sphere indicated the same kind of change, i. e. from hot to cold ; but it will be observed that the changes are quite the reverse. The sedimentary beds of equatorial America contain shells analo- gous, and some identical, to those found only in the south tempe- rate zone, and none indigenous to the seas of the northern hemi- sphere. Those who may prefer the doctrine of a cooling globe to account for the phenomena, are placed in the dilemma of making the globe hot only in the northern hemisphere and colder at the tropics than at present to agree with the observed facts. The variable temperature on the surface of the globe is pro- 76 duced by solar radiation in connexion with the modifying effects of the atmosphere: we have no reason to suppose that climate has ever been governed by any other source of heat. In order to understand the general nature of the present climates from pole to pole, let a convex lens be exposed to the rays of the sun, the rays will be concentrated into the focus, and cause intense heat ; the degree of heat depends on the number of rays col- lected and concentrated into the focus. If we expose a small point to this focus it would be intensely heated ; but if, in- stead of a point, we place a large body in the focus, the heat would be diminished, and the nearer we approach the lens the less the heat. Our globe occupies the focus of the atmospheric lens, illus- trated in Plate XX., and thus prevents the concentration of the sun’s rays into one point. In the equatorial region, when the sun is in the zenith, if we ascend to the height of 20,000 feet, instead of finding it hotter as we rise, we get into colder regions, 2. €. perpetual snow. Hence it follows that one planet may be near the sun, and another placed at the confines of the solar sy- stem, and yet both possessing equal temperature on their sur- faces, by proportioning the diameter of their atmospheric lenses to that of their respective bodies. Therefore to say that Venus must be intensely hot and that Saturn is in the region of eternal snow, 1s a mere assumption, unsupported by analogy. Some attempts have been made to show how the globe may have be- come hot and cold by its probable exposure to the effects of intense stellar radiation in passing through the milky way; but such speculations are flights of the fancy, and unworthy of atten- tion. There has been too much dependence placed on celestial observations already for the progress of geology. If we would speculate to any purpose on a former state of our globe, and on the succession of events which from time to time have changed the condition and form of its surface, we must confine our principal inquiries to the results or effects of terrestrial physics, and not attempt to solve the problems by reference to celestial objects; for if we differ so materially on those points which we can handle, it is not probable that we could decide by referring to objects so much beyond our reach. We shall give a few examples of some points used by geolo- gists for their guidance in theoretical researches, founded on 77 astronomical observations, which are not only doubtful, but proved incorrect. It is said that the moon turns on her own axis, because she is an oblate spheroid, notwithstanding that she always presents the same face towards the earth. That a body revolving round a centre, and continuing to present the same face to that centre, should rotate on an axis situated parallel to the revolving axis, is physically impossible. Yet it is main- tained, and absolutely stated in our astronomical works, that the moon rotates on her axis. There is another idea propagated respecting this body, viz. that she has no atmosphere, because we do not observe any re- fraction during the occultations of the stars. If the moon is enveloped in an atmosphere, the angle of refraction would be between the moon and the star, and that would, on impinging on the moon’s surface, be reflected towards the earth. Ifa ray of light be successively transmitted through several transparent media having different refracting powers on one side, and re- flected so as to pass through similar media on the other side, its emergence from the last of these media will take a direction parallel to that which it had when incident upon the first of them. In this case the several refractions which the ray suffers in passing through the media on the one side is compensated and neutralised on the other, so as to produce, on the whole, no deflection of the ray from its original course. “The angle of in- cidence is equal to the angle of reflection.” The reason why we observe the refraction of the rays in our atmosphere is, because we are exposed to one angle only, 4. e. that of refraction, owing to our being within the spherical media. Yet we are told the moon has no atmosphere, because she does not show signs of refraction, notwithstanding the contrary evidences proved by the halo which this body often exhibits. Persons have attempted to describe the geological features of the moon! If the above simple questions are in such a confused state, and so easily de- monstrated at a distance by the aid of mathematics, what are we to expect from the geology of the moon? Unless geologists can procure more substantial data than those obtained from celes- tial observations, it is not very probable that the science can im- prove ; and much less when fettered by other incompatible laws, which have taken too deep a root to be very easily eradicated. The changes of climate have been attributed by some to a 18 greater excentricity of the orbit formerly than it is at present. But even the excentricity of the orbit is a doubtful question; the only proof brought forward that the orbit is excentric is the variable diameter of the sun. The atmospheric lens not only refracts the rays when not in the direction of the radius, @. e. in the zenith, but also augments the size of bodies, such as the sun, the maximum size being in the horizon and the minimum in the zenith. According to a series of observations made by the author for nine years within the tropics, the sun’s apparent diameter is throughout the year the same when measured in the zenith; therefore its observed variable diameter is an optical deception, and not from any excentricity of the orbit. That this is the case must be well known to those who have taken observa- tions in the southern hemisphere with delicate instruments, and especially when the diameter of the sun formed an important amount in the measurement*. To return from this digression, we find that the variable nature of climates from pole to pole arises principally from the obliquity of the rays and the height from the sea, and not from internal heat; * Santa Ana, N.L. 5° 10/0”. The sun’s diameter, according to direct ob- servations taken in the meridian from the south tropic to the north. South tropic ......... =< 61° 22' 37" altitude. 31! 30” diameter. ASQUALOT oc c0t.vescesiess 84 50 0 Be 30 45 ro Tra BE? 8 po eogiO UNE, 30, 36n) North tropic ......... 71 35 20 4s 31 12 55 The following measurements exhibit the apparent variation of the sun’s diameter in the plane of the orbit during its daily apparent path, from the rising to the setting; the latitude of observations and the sun’s declination being equal. - Diameter. Diameter. The sun rising < 0° 32! 55" Noon 8S. in zenith <90° 30! 36” ps I> 182.35 . 75. | Se . 30 32 18 Me 60 31 30 - 45 81 55 3 45 381 50 Ls 60ngws ge - 30.82.45 S en ee 15 32 32 39 The sun setting ... 0 32 51a If it is maintained that the orbit is an ellipse, because the sun appears larger at a lower altitude in December than in June at a higher elevation ; on equally good data we may state that its diurnal path is an ellipse, and that our approach to the sun morning and evening is compensated by the obliquity of the rays and greater velocity, thus forgetting the consequence of such de- ductions at those places under the sun in the opposite hemisphere. When Kepler established the excentricity of the earth’s orbit little was known of re- fraction. 19 therefore we can only account for the changes of climate indi- cated by the organic remains by changes in the relative position of the dry land and the sun’s rays. Professor Lyell suggested that the changes in the position of land and sea may have given rise to the vicissitudes in climate. The Professor does not bring proofs of more than a mere rise and fall of land from the level of the ocean, which could not furnish us with tropical heat in the arctic regions, therefore he assumes the possibility of geographical changes, such as the shifting of land from the southern hemisphere to the northern, to reconcile the effects with the facts. ‘“ However constant,” says the same author, “may be the relative proportion of sea and land, we know that there are constantly some small va- riations in their respective geographical positions, and that in every century the land is in some parts raised and in others de- pressed. By these ceaseless changes the configuration of the earth’s surface has been remodeled again and again since it was the habitation of organic beings, and the bed of the ocean has been lifted up to the height of some of the loftiest mountains. The imagination is apt to take alarm when called upon to admit the formation of such irregularities in the crust of the earth after it had once become the habitation of living creatures; but, if time be allowed, the operation need not subvert the ordinary repose of nature, and the result is in a general view insignificant, if we consider how slightly the highest mountain chains cause our globe to differ from a perfect sphere. Chimboraga, though it rises to more than 21,000 feet above the sea, would be repre- sented, on a globe of about six feet diameter, by a grain of sand less than one-twentieth of an inch in thickness.” Let us consider what would be the nature of the deposition in a large tract of land like Australia, supposing it gradually floated from its present position to the north polar region. Here and near it, tree ferns, Cycadez, Araucariz, Cassiarinz grow upon the land: corals and sponges abound on the coast even of Van Die- men’s Land; also Trigonia, Cerithium, Isocardia, a Cardium like C. hillarium of the greensand, and quadrupeds of the pe- culiar marsupial races, to which the Stonesfield animal is re- ferred by Cuvier. These would be deposited, and their place would become gradually occupied by others as it approached the equator, where it would be inhabited by a different variety. 80 These would again disappear on the arrival of the land in the north, and their place would be taken by others. The contents of the deposition, supposing the land undulated above and below the level of the sea during its movement from the south to the north, would represent the order of deposition and organic remains similar to those now found in the rocks of the northern hemisphere. CHAPTER XIII. THE DIVISION OF THE SURFACE OF THE GLOBE INTO ZONES OF DEPOSITION. Ir, as we have endeavoured to establish, the sedimentary rocks have been deposited in different zones during the movement of the surface from the south pole towards the north, we may distinguish their respective zones of deposition in the following order :— Zones. Deposits. No. 1. South frigid . . The most ancient :—Cambrian and Silurian. 2. South temperate . The Carboniferous, or great coal formation. 3. South tropic . . Oolitic, or Saurian group. 4. North tropic . . Cretaceous, & tertiary of Europe. 5. North temperate . Alluvial deposits of Europe. 1. Commencing with the most ancient deposits, we find Or- thoceratite, Trilobite, and other marine relics, but scarcely any land plants. That this ancient deposit should not contain land plants is not surprizing. The newly-discovered countries within the south frigid zone, although placed in latitudes in which herds of wild herbivoro s animals are met with in the northern hemi- sphere, nay, where man himself exists, are most wintry in their aspect, almost entirely covered with ice and snow even in sum- mer, and completely destitute of animal life and vegetation. The living representatives of the fossils have not yet been identified ; but according to Dr. Buckland, the nearest approach 81 among living animals to the external form of Trilobites is that afforded by the genus Serolis in the class Crustacea. The genus Serolis inhabits the Straits of Magellan and the coast of Pata- gonia. The beach is often seen covered with them dead; they are found alive only by dredging in deep water. This region is but little known, but the above approximation is sufficient for our present purpose. All the deposits found within this region are comparatively recent, containing organic remains of those only which inhabit the bordering sea. 2. South temperate deposits, or Carboniferous groups. The forms of life buried in this system of strata are exceed- ingly numerous and varied, and generally in an excellent state of preservation, allowing of a most strict comparison with exist- ing types. They consist of many races of plants, abundance of Zoophyta, with multitudes of Mollusca, Crustacea and Fishes. The plants are in some respects very similar to existing races, as the large group of ferns generally, the Equiseta, Lycopodiacee, Araucaria, Cycadez, Coniferz, &c. The remains of these plants are often abundant in coal-seams. The coal plants of North America are for the most part identical with those of Europe, and all belong to the same genera. Specimens from Greenland are referrible to ferns, analogous to those of our Kuropean coal mines. The fossil plants brought from Melville Island warrant similar conclusions. The coal formation of Bogota, which is situated within 4° north of the equator, at an elevation of about 8000 feet above the level _of the sea, contains the same kind of plants —arborescent ferns, and Lycopodiacez of the same species as those now growing in the southern hemisphere. The living representatives of the above are found in New Holland, New Zealand, Brazils, Chili, and va- rious islands within the south temperate zone. Not a single species of Cycadez is known to grow in the north temperate region ; their principal localities are equinoctial America, and southward of that part, the Cape of Good Hope, Madagascar, India, the Molucca Islands and New. Holland. The enlarged size of the arborescent ferns depend not only on a warm temperature, but also on a shady and moist place. Within the tropics they are found at an elevation of about 4000 feet above the sea, from twenty to thirty feet high, flourishing G 82 only in shady parts of great humidity. It is in the south tem- perate zone of America that the ferns approach to the mag- nitude of those found in the European coal formation. Trees grow in this region to a very large size, and the shrubs and smaller plants become particularly luxuriant and productive. Much alluvial matter, saturated with calcareous and siliceous solutions, is carried down the valleys, blended with decomposed vegetation, and forming immense deposits. Springs of bitumen are also very abundant, and form very extensive beds. Were persons a little more acquainted with this prolific re- gion, and possessed more information respecting the great deposits of calcareous, siliceous, bitumen beds, &c. which are now forming and consolidating in a short period, they would not be quite so extravagant in their calculations on the time necessary to form the coal formation *. Small beds of lignites are formed within the tropics in less than one hundred years in favourable situations, and more especially in the neighbourhood of bituminous springs. Owing to the great warmth, rich and soft nature of the soil, tender plants flourish through the long winters of Patagonia. The humidity of the air near the Straits of Ma- gellan is very great, yet there is great warmth in the sea and in the soil. There is no well-authenticated instance of the remains of a saurian animal having been found in a member of the carboni- ferous series of England; nor have the bones of any terrestrial mammalia been discoveredt. Their absence has been regarded by some as corroborating the theory of the non-existence of the — higher orders of animals in the earlier ages, but the circumstance is owing to the geographical position of the zone; the general character of this division of our globe being a profusion of vegetation, and land almost destitute of quadrupeds. “ Ker- guelen’s land, which is of no inconsiderable size, placed in lat. 49° 20! south, and also the groups of fertile islands in the Pacific Ocean, contain no quadrupeds, except such as appear to have been conveyed there by man. Even the islands of New Zea- * It has been calculated that the coal series of Newcastle, with its accom- panying strata, must have required for its production a period of at least 200,000 years. t+ Traces of reptiles have been found in other countries. 83 land, which may be compared to Ireland and Scotland in di- mensions, appear to possess no indigenous quadrupeds except the bat; and this becomes the more striking when we recollect that the northern extremity of New Zealand stretches to latitude 34°, where the warmth of the climate must greatly favour the prolific development of organic life *.” 3 Australia is exceedingly deficient in Saurians and other ter- restrial quadrupeds. Hence the contents of the carboniferous group accord well with the prevalence of such a state of things in the southern hemisphere during their respective depositions. We cannot expect to find any large coal formation south of the tropics, but mere beds of lignites ; because should there be any forming it would be below the level of the sea, and not yet sufficiently consolidated to make good coal. The coal forma- tion of Australia is a similar new formation. “ In the inlet of Awaaba, in 33° south latitude, is a formation of conglomerate and sandstone, with subordinate beds of lignite, which extends from the Hunter river southwards towards Brisbane water. The lignite constitutes the so-called Australian coal f.” Tree ferns, which require abundance of moisture and an equa- lization of the seasons, are found in Van Diemen’s Land in south latitude 42°, and in New Zealand in south latitude 45°. The orchideous parasites also advance to the 42° south latitude. Before concluding this part of our inquiry, we shall make a few observations on the supposed predominance of carbonic acid in the atmosphere during the deposition of the coal-beds. The researches of M. A. Brongniart on fossil plants led him to conclude that during the early period, when the plants entombed in the coal-measures of the northern hemisnhere flourished, the atmosphere was more charged with carbonic acid than at pre- sent, aiding, it is said, the development of the gigantic species seen in the coal, and also protecting them when dead from bemg so readily decomposed by the atmosphere. It is difficult to conceive how the idea of plants obtaining their carbon from the atmosphere originated, when it is a well- known fact that it is obtained from the soil. No such atmo- sphere exists in the southern hemisphere, nor within the tropics, * Lyell, Principles of Geology, vol. i. p. 199. f Geological Proceedings, March 8th, 1843. 84 yet those magnificent trees above alluded to grow there; but the soil is strongly impregnated with carbonic acid. It is more or less saturated in all soils, and without it vegetation cannot thrive, as it feeds the plants by means of the roots, and not by the leaves. The function of the leaves is to evolve the gases, i. €. they form the negative plates to the currents of sap in the living plants. Had there not been a provision to take the car- bonic acid away from the atmosphere we could not exist; in- deed it is the absence of it from the air that preserves the vital principle. The purer the air is at the leaves, with a due pro- portion of moisture, the more healthy is vegetable life *. Probably our coal-beds may be as much due to the combina- tion of carbonic acid and hydrogen forming bitumen, as they are to decomposed vegetation. We have abundant facts to prove that plants are as liable to become silicified as to be converted into coal; and there are also proofs of beds of lignites forming from bituminous substances, near the roots of living plants, within the tropics. We shall not enter into a description of the probable mode of deposition of the carboniferous series, because this has been well explained in all geological works; but we may note in con- clusion, that the coal basins appear to be principally lacustrine deposits, where bitumen, mud, sand, and decomposed vegetable matter may have accumulated, such as we now see forming within the tropics and in the southern hemisphere. 3. South Tropical Zone. The system of rocks between the car- boniferous strata and the chalk, containing a large propor- tion of gigantic amphibious Saurians. The oolitic group may be considered as representing this di- vision of the series. The remains of plants, Zoophyta, Mollusca, Articulosa, and vertebral animals belonging to the oolitic system, * The respiration which takes place at the leaves has been found to vitiate the atmosphere, and more especially at night; the sun’s rays appear to restore the purity of the air. An atmosphere containing 60 per cent. of carbonic acid gas has been found destructive of vegetable life ; the doses become less preju- dicial as they are diminished. Any addition, however small, of this gas to common air, if placed in the shade so as not to be neutralized by the sun’s rays, has been found prejudicial to plants. 85 are very numerous. ‘The most characteristic of the plants are the group of Cycadez, of which stems in the isle of Portland, and leaves and fruit in Yorkshire, show considerable analogy to the existing forms of the tribe at the Cape of Good Hope, in India and Australia. The sponges resemble those of New Holland. Among the Saurians, those which frequented the water predominate in number, but the largest forms were terrestrial (Iguanodon, Me- galosaurus). It is interesting to know that the earliest Mam- malia, of which we have yet any trace, were of the marsupial division now almost characteristic of Australia, the country where yet remain the Trigonia, Cerithium, Isocardia, Zamia, tree- fern, and other forms of life so analogous to those of the oolitic periods. During the deposition of the European formation the rivers and shores were inhabited by Saurians more or less am- phibious, while the sea was full of forms of Zoophyta, Mollusca, Articulosa and Fishes. Within the south tropical zone we find a similar scene of or- ganic life in the seas, lagoons, and on land enjoying their limited existence. Here the rivers, such as the Amazon and its shores, are watched by amphibious Saurians, the living representatives of the Megalosaurus and Iguanodon. Although the identical species have become extinct, yet the alligator, crocodile, gavial, and the bavial of South America (the latter was seen by the writer in the lagoons of equatorial America, having a head like an iguana and a body like a crocodile), are sufficient to show the corre- spondence of this zone to the fossils of the oolitic group. When we consider the myriads of reptiles which inhabit this zone, it is not surprising that their relics should be found in sediments within their own element; nor is it to be wondered at that no traces of man and his works have been found in such deposits. There are regions at present in the Indian and Pacific Oceans co-extensive in area with the continents of Europe and North America, where we might dredge the bottom and draw up thousands of shells and corals without obtaining one bone of a land quadruped. The casualties must always be rare by which land quadrupeds are swept by rivers far out into the open sea, and still rarer the contingency of sucha floating body not being devoured by sharks or other predaceous fish. If the carcass 86 should escape and happen to sink where sediment was in the act of accumulating, and if the numerous causes of subsequent disintegration should not efface all traces of the bedy, is it not contrary to all calculation of chances that we should hit upon the exact spot? Can we expect for a moment, when we have only succeeded amidst several thousand fragments of corals and shells in finding a few bones of aquatic or amphibious animals, that we should meet with a single skeleton of an inhabitant of the land? Are we then warranted in supposing that man was not an inhabitant of this world during the deposition of the oolitic group? In the first place, the southern hemisphere is even at present but thinly inhabited, and if perchance a man be car- ried into the rivers, he would soon be devoured amongst such a profusion of carnivorous reptiles. As to the works of man within this zone, even at the present advanced state of civilization, they consist of such materials that their remains would be undistin- guishable from the wrecks of the forest. Therefore we have no proof that man was not an inhabitant of this world during the deposition of the series in question. Let us take as an example the banks and lagoons of the Amazon, which are swarming with reptiles, and consider the na- ture of the deposits forming at the mouth of this immense river. The inhabitants of the country are principally roving Indians, living in bamboo huts; probably we should not be far wrong in stating, that for every man there are within this region 10,000 amphibious animals. Again, for every man, or his relics, which may be carried into the deposits of the river and escape being devoured, there will be deposited 100,000 amphibious reptiles : is it then to be wondered at that man or his works have not been discovered in the deposits of the saurian zone, much less during past «eras, before the world became so thickly populated as it is at present? Besides, the deposits in question have been but very partially explored,—merely the edges of the strata. Marine animal life was exceedingly abundant during the de- position of the older oolitic group now found in Kurope; some beds seem composed of little else than the remains of shells and — corals. A very striking zoological feature of this group is the immense abundance of Ammonites and Belemnites which must have ex sted previous to, and during not only the deposition of 87 the European group, but also when the most recent equivalent of the same group was formed, as now seen near the equator. It would far exceed our limits to enter into the general com- parison which might be made, even to minute details, of the living representatives and the depositions of the river Amazon, and other parts within the south tropical zone, with the fossils and deposits of the oolitic group; and as it only forms but a mere link in our chain of argument in support of the northward movement of the surface, we must content ourselves with a ge- neral glance. If this system of deposits was formed within the south tropical zone, and should they be visible at the equator, they must be very superficial, and in a very unconsolidated state as compared with the European. The equivalent of the Kuro- pean oolitic group in eguinoctial America, from the Amazon to the Orinoco, and on the plains and table-lands of New Grenada, is an immense mass of alternate beds of fine-grained quartzose sandstone and conglomerates, containing Ammonites, Belem- nites, and a variety of other marine shells, together with species of fossil plants of the Cycadez, Coniferz, &c.; ,and on the super- ficial, arenaceous and unconsolidated part of the same series are found immense bones, considered to be the remains of the Mastodon. ‘These bones are very abundant in the province of Nieva, amongst which are those of the alligator. In New Grenada this series of sandstone is stratified in layers more or less horizontal; a great number of the thinner and upper seams are composed of decayed leaves and impressions of plants the same as those now growing on the spot. On the plains of Mariquita and Nieva are immense isolated terraces pre- senting beautiful sections of 2000 feet high; and also on the plains of Bogota, resting on the coal formation of that district ; whilst on the west this formation rests immediately on the cry- stalline schists of the central Cordillera. The elevation of this part of South America from the level of the sea (which appears to have been comparatively recent) was extremely uniform, and about 3000 feet. According to the theory here brought forward, it was not a mere vertical rise, but a diagonal movement from the south. There are but few beds of the oolitic group suffi- ciently consolidated for building stones, and those that are so em- ployed are much softer than the common freestone. Stems of soft plants are commonly found, as black as jet, in the harder beds. 88 In examining recent deposits within the tropics, we often find the accumulations of only a particular variety of plants : and it is remarkable that some plants which are common in the neigh- bourhood are yet absent in the deposits. Some appear more susceptible to rapid decay than others; hence it follows that if a series of beds should be found to contain only a particular class of plants, it is no reason but that other kinds grew, not only in the region but within the district. We note these facts in order to guard against the too hasty conclusions of supposing that the fossils always represent the real character, number and variety, of the living organie system during their deposition. 4. North Tropical Zone.—The European, Cretaceous and Tertiary : Deposits. Although the English sedimentary rocks are divided into di- stinct groups, it is not a natural and definite subdivision, but depending entirely on local circumstances. A perfect transition from one bed into another is of more common occurrence in nature than distinct separation. We have no cretaceous equiva- lent in the equatorial zone; nor can we expect to find such a deposit, if as we suppose, this is a marine formation, formed in that part of the globe. No remains of mammiferous animals have been discovered in the cretaceous series of England, and the exuvie of reptiles are by no means common, showing that the deposit was formed somewhat distant from dry lands. The re- mains of a crocodile have, however, been found in the chalk of Meudon, and the exuvie of a large reptile, the Mososaurus, at Maestricht. The remains of fish are not so rare. The supracre- taceous deposits are commonly termed tertiary, which denomi- nation is exceedingly objectionable and inapplicable, as it implies that there were three classes of rocks possessing marked charac- teristic distinctions, and that the deposits above the chalk con- stituted the third of such classes*. We should rather consider, that as other groups pass into each other in one place, while there is evidently a geological break between them in another, that the like should happen with respect to the cretaceous and supracretaceous groups. In examining the deposits which are now forming within the tropical region, we often find a great number of beds containing * De Ja Beche’s Geological Researches, p. 355. 89 only marine and freshwater organic remains, and it is but in very few instances that we can detect traces of terrestrial crea- tures. In some parts, large deposits of carbonate of lime are seen, with scarcely any organic remains, although forming at the same time as those deposits in which they are very abundant. Those persons who confide in what are hastily called general views, and believe in the gradual change and sequence of organic life on the globe, and picture to themselves the early land and sea as tenanted only by what they find in the sedimentary deposits of a particular region, from what they consider simple forms of life to a more complicated, till man, as they say, was at last awakened to the supremacy of creation,—would receive a useful lesson on the banks of the river Magdalena and the lagoons of Santa Martha; they would soon be satisfied that the few fossil birds and quadrupeds of Stonesfield, and other places, are not anomalies so puzzling as they were once considered. How can we expect to find the whole variety of the living system in such deposits? It is as unreasonable as the general views which have been established on their absence. Although there have been actually found, not only the bones of quadrupeds, and various terrestrial animals, but also those of man, amongst those of the extinct animals, in caves, &c., and also in a fossil state in the calcareous deposits of Guadaloupe, yet so obstinate is the adherence to the supposed recent origin of man, as compared with the organic remains of the sedimen- tary rocks, that such discoveries are not considered sufficient to prove their coexistence. Various species of monkeys have been found under similar circumstances, which were at one time con- sidered of the same recent origin; even this must show the in- consistency of the hypothesis. In the red sandstone, which occupies nearly the same geological position as the cretaceous group, m Dumfriesshire in Scotland, and Massachusetts in North America, we find the impressions of the feet of birds, and the foot-marks of tortoises. On the pre- sent soft sand banks of the river Magdalena, between Mompox and Morales, the writer saw impressions of foot-marks of birds of a most gigantic size,—feet measuring about fourteen inches long and eight inches wide, having three claws, and the steps four feet; amongst which were also those of tortoises, and various 90 other animals well known on the banks of the river. Although the bird itself has not been seen, there can be no doubt of its existence, as the impression was found in the soft bank in the middle of the river, which a heavy storm would obliterate, amongst other well-known species. The trees in the dirt-bed in the neigh- bourhood of Weymouth stand in or rest upon the soil in which they grew; consequently their submersion beneath the water in which the Purbeck beds were formed, and which now cover them, must have been gradual and unaccompanied by a rush of waters. Such is the case in the present formation of their equi- valent in the lagoons of Santa Martha, where the trees are grow- ing in shallow water, subject to slight oscillations above and be- low the level of the sea. Sometimes the salt water prevails, and the sediment becomes thickly covered with marine shells: during the great floods pouring down the Magdalena, carrying with it immense forests and the debris of rocks, the lagoons become again covered with freshwater and terrestrial organic remains. Thus, by variable seasons, and by the slow oscillation of the land by sub- terranean forces acting for a long period, the variable sedimen- tary beds are formed, such as we now see them when exposed to view. Lacustrine deposits of the same period may present very different characters, depending on the nature of the locality in which they may be formed: for instance, the lagoons of the Orinoco may contain a very different series of organic remains, as compared with those of the Magdalena; hence formations may be of the same age and the same zone, yet different in de- grees of induration and organic contents, as well as in the rela- tive geological position. Viewed generally over a considerable area, the rock called chalk is based either upon an arenaceous or argillaceous deposit. As we cannot expect uniformity in the distribution of detritus, unless under conditions which could scarcely ever obtain, we should anticipate that sands would pre- dominate over one part of the area and mud or silt over another, as we now find to be the case in the present deposits forming within the tropics. The white variety may probably have re- sulted from the precipitation of carbonate of lime from solution in water, in a favourable locality, suitable for the reception of calcareous springs. The supracretaceous group of Europe completes the great sedi- 91 mentary system of rocks; during the deposition of which it has been supposed man came into existence, simply because his remains are principally found in the superficial part of the series. These rocks constitute a large proportion of the dry land of Europe; and there are abundant evidences that they are, com paratively speaking, of recent origin, and that a great por- tion of the dry lands now forming Europe and Asia, have been raised from the sea since they were exposed to a hotter climate. The chalk of Europe, the oolite of the tropics, and the coal formation of the south temperate, may be all of the same age; hence it will be observed that the present mode of distinguish- ing these rocks is only applicable in certain localities, in the same parallels of latitude. Sir H. De la Beche very justly remarks that “ classifications entirely founded on organic remains are at al] times lable to be erroneous, if contemporaneous deposition be thence inferred as a necessary consequence, as we have had occasion to observe ; they therefore may be considered as doubly liable to error when employed in proving contemporaneous origin in such rocks as those of the supracretaceous period.” Palms and crocodiles are found in these deposits, analogous if not identical to those now found in Africa and in the neigh- bourhood of the Nile. That a great number of organic beings should have become extinct during such great oscillations of the earth’s surface is a very natural supposition ; it is more surpri- sing that so many of the grand stock should have been preserved amongst the numberless vicissitudes of climates, and the sepa- ration of continents into islands, and vice versa. The last group of sedimentary beds pass so insensibly into the superficial alluvial deposits that no line of demarcation can be drawn; we shall therefore close this subject by observing, _ that the alluvial and loose accumulation of sands, &c. covering the indurated sedimentary beds in Europe, contain principally organic remains belonging, or indigenous, to the zone in which they are now found. As this part of the subject is so well described in almost all geological works, we must beg refer- ence to them, trusting tHat the outline we have given here is sufficient to show the agreement in the order of the sedimentary rocks with the action of the northerly movement ot the magnetic 92 currents, and that this prime mover, which controls our planet, is equally available to guide us in our researches in sedimentary rocks as it is in the fundamental series and mineral] deposits. CHAPTER XIV. ON THE GENERAL NATURE OF THE DISTRIBUTION OF HEAT OVER THE SURFACE OF THE GLOBE, AND THE ZONES OF EQUAL TEMPERATURE. In order to avoid misconception with respect to the zones, and not to suppose that they are considered here as parallel bands, such as those mathematically drawn on our artificial globes, we introduce these observations to explain their general character, and their influence on the organic system. It is now well ascertained that zones of equal warmth, both in the atmosphere and in the waters of the ocean, are neither parallel to the equator nor to each other. It is also known that the mean annual temperature may be the same in two places which enjoy very different climates, for the seasons may be nearly uniform or violently contrasted, so that the lines of equal winter temperature do not coincide with those of equal annual heat. The deviations of all these lines from the same parallel of lati- tude are determined by a multitude of circumstances, among the principal of which are the position, direction and elevation of the continents and islands, the position and depths of the sea, and the direction of currents and of winds. The amount of the immediate solar heat depends upon the position of the sun in the ecliptic, the direction in which the sun’s rays strike the earth, and the variable degrees of intensity occasioned by the atmospheric lens, illustrated in Plate XX. In proceeding from the equator towards either of the poles, with- out altering our height above the level of the sea, we must travel a great distance before we find the mean annual temperature reduced even a few degrees; but by increasing our elevation, a rapid change of temperature will be experienced, till we arrive 93 at the point where constant frost prevails, i.e. the curve of con- gelation. (See Plate.) The annexed table shows the relative height of this curve in different latitudes from the level of the sea :— Height of Curve Mean temperature Latitude. of Congelation. at the level of the sea. 0 16,000 84°2 Fahr. 10 15,600 82°6 20 14,500 78°1 30 12,600 711 40 10,000 62°6 50 6,900 53°6 60 3,900 45°0 70 1,000 38°1 80 O 32:0 What we have stated above respecting the variable tempera- ture of the sub-aérial zones according to the heights, we have every reason to suppose is applicable to similar sub-aqueous zones of variable temperature from the level of the sea down- wards. At the equator, commencing from the level of the sea upwards, we have the following :— Mean temperature. Level of the sea 84°. 4,000 feet high 70°, descending to the level of the sea in 30° lat. 8,000 32 62 32 2) 39 29 40 12,000 5 44 29 0 0 > 60 I 6,000 32 3 2 29 33 29 39 80 From the level of the sea downwards the temperature decreases in a similar manner, but the actual variations of temperature in the sub-aqueous zones are not known. All that is positively ascertained is, that within the tropics the ocean is found to be getting colder as we descend. According to the concentrated rays, the heat of the sun ought to increase in depth, and such would be the case in an empty space; but liquids conduct heat very imperfectly downwards. A thermometer let down a few feet below the surface of a pond or of the sea, would, on being drawn up, indicate a lower tempe- rature than that of the surface water; for the latter, heated by the rays of the sun, would communicate by conduction little or 94 no heat to the water below. Indeed it can be proved by experi- ment, that water does not transmit heat downwards by conduc- tion ; whereas, in applying heat underneath instead of to the sur- face, it is easily transmitted. Had the globe contained .an igne- ous nucleus, whatever might be the bad conducting quality of the crystalline shell, it would be heated, and that heat would be communicated to the ocean, and an ebullition would be produced sufficiently strong, if not to cause evaporation of the ocean, at least to prevent the formation of ice at the poles, and the heat would increase as we descend. The observed facts are quite the reverse. It is very probable that the ocean at a cer- tain depth possesses a constant temperature, and according to observations made in the polar regions on the temperature of the ocean under the ice at the depth of 100 fathoms, we may con- sider it about 45° Fahr. We may appeal to observations for proof that it is at the surface of the globe the greatest variations of temperature take place, and from this surface they diminish as we ascend into the air or descend into the ocean, till in each direction they terminate at an invariable temperature, where the solar radiant heat becomes insensible; and it is within these zones of variable temperature that the animal and vegetable .kingdoms are bounded. According to the above, we find that in sailing from the south pole to the north we are exposed to zones of variable tempera- ture: commencing at 32° Fahr., and on arriving at the equator, it amounts to 84°°2, and becomes reduced again as we approach the north pole to 32°. If, instead of sailing on the ocean, we sail through the air at the elevation of the above curve, we should be constantly exposed to the low temperature of 32°. The vari- able height of the land between the level of the sea and the curve of congelation must therefore vary the climate of the different zones, independent of their latitudes. Within the tropics we may obtain any temperature from 84°2 to 32°, by regulating our elevation; but in the frigid zone we are limited for the want of direct rays, and cannot obtain a mean temperature above 50° by depression, or by any other means we may choose to adopt; consequently no changes in the relative position of land and sea can produce a tropical climate in the polar zone. ‘The aspect of a country has an influence upon its climate, for this reason, that the angle at which the sun’s rays strike the ground, and conse- 05 quently the power of those rays in heating it, varies with the exposure of the soil relatively to the sun. Countries in the northern hemisphere will be rendered warmer by having large tracts of low land to the south and sea to the north, and cooler when the relative position of these two is reversed. This fact is exemplified by a comparison of the climate of Europe with that of America and Asia. The western parts of the old conti- nent derive considerable warmth from Africa. On the contrary, the north-eastern extremity of Asia experiences in the same lati- tude extreme cold; for it has land on the north between the sixtieth and seventieth parallel, while to the south it 1s separated from the equator by the North Pacific. ‘The whole of Europe, compared with the eastern parts of America and Asia, has an insular climate. If lines be drawn round the globe through all those places which have the same winter temperature, they are found to deviate from the terrestrial parallels much more than the lines of equal mean temperature. When we compare the climate of the northern and southern hemispheres we find a great difference in the corresponding parallels. There is no accurate information as to the mean tem- perature of any place beyond 50° of south latitude; but there is every reason to suppose that it differs considerably from that of places in the same degree of north latitude. In Sandwich land, according to Cook, in 59° of south latitude, the perpetual snow and ice reach to the sea beach; and in the island of Georgia, which is in 54° of south latitude, the line of perpetual snow descends to the level of the ocean. We therefore observe that latitude is one only of many powerful causes which determine the climate of particular regions of the globe. The coldness of the southern hemisphere in countries situated under similar cir- cumstances as those in the north, has frequently been attributed to a cause quite inadequate to explain it, namely that of the sun being a shorter time (said to be 73 days) on the south than on the north side of the equator. As the variable diameter and ve- locity of the sun has been already alluded to as optical decep- tions, we need not dwell on the inadequacy of such an hypothesis to account for the difference, but simply state, that we believe the lower degrees of temperature of the southern zones as com- pared to those of the north, placed under equal circumstances, 96 arise from the northerly movement of the ocean. Ice has been seen floating in the southern hemisphere between latitudes 36° and 39°. Having thus noticed the subject of temperature, it will be proper to advert to the amount of moisture which the atmo- sphere contains in different parts of the globe. In the tempe- rate zone, with a mean temperature of 523°, the annual evapo- ration has been found to be between thirty-six and thirty-seven inches. At Cumana, on the coast of South America (north lat. 104°), with a mean temperature of 81°86 degrees, it was ascer- tained to be more than 100 inches in the course of the year; at Guadaloupe, in the West Indies, it has been observed to amount to ninety-seven inches. The average yearly quantity of rain is greatest within the tropics, and it seems to diminish the further we recede from the equator. In general much more rain falls in mountainous countries covered with extensive forests than in those where wood is less abundant. The following shows the quantity of rain fallen at Marmato, on the western Cordillera, latitude 6° 28’ north, elevation above the level of the sea 4836 feet, mean temperature about 68°, from the year 1833 to 1841 inclusive. 1833. 1834. 1835. 1835. 1837. Tns. rr Ins. - Ins. is Ins. Ins. Ett Jan. to March...| 15°15 5°15 95:14 oaa5 8°] April to June...| 24:3 29-6 34:6 39°4 23:9 July to Sept. ... 20 ey) 21:2 18:3 18°1 Oct to Dees <2.) 178 24:12 - 36°14 28°10 31:16 59°6 WEE 127°16 99:0 81:7 1838. 1839. 1840. 1841. cau es Ins a Ins, mf Ins. Jan. to March... 21:10 10°16 18°3 12°3 April to June... 41:18 28:0 220 26:2 July to Sept. ... 19-0 23°16 9:3 16°35 Oct. to Dec. ... 31:0 31:18 14:17 32°2 113°8 94:10 64:3 87.2 It must not, however, be imagined that the climate of all hot countries is characterized by such abundant rains; for there are many which from one year to another are either almost or 97 entirely destitute of rain. This is the case along an extent of several hundred miles of the coast of Peru, and many other parts. At Cumana, on the north coast of South America, the annual quantity of rain is scarcely 10 inches ; and there are other places on the shores of that continent where none falls for several years, but where, nevertheless, vegetation is exceedingly luxu- riant, owing to the humidity of the atmosphere. In Santa Ana, on the central Cordillera, at an elevation of 3648 feet above the level of the sea, mean temperature 75°, lati- tude 5° 10! north, no rain falls for months together, yet the air is so strongly saturated that vegetation (excepting the plains below) flourish in their usual luxuriance. In the torrid zone, generally, the temperature ranges within comparatively small limits, and the various phenomena of the atmosphere occur from one year to another with a regular and uniform succession un- known in this part of the world: the dry and rainy seasons are the divisions of the year, depending on the position of the sun and elevation. The subject of climate is in itself highly interesting ; but it be- comes still more so when we extend our view, and consider its effects upon the numerous animal and vegetable tribes which are dispersed over the earth, and compare them with those of the past, which are now entombed in our rocks. Every climate, as we pass from the plains just raised above the level of the ocean to the curve of congelation, has its pecu- liar vegetation. At the equator palms flourish within the zone, varying from 80° to 70° of mean annual temperature; but on ascending to the elevation of 4000 feet above the level of the sea, to a mean temperature below 70°, they almost cease to grow; however, a few isolated groups of particular species con- tinue to flourish at a higher elevation in New Grenada. On ascending to the elevation of about 5000 feet the arborescent ferns cease to grow, and in the next zone (above) the vegetable tribe of the hot region disappears, and new varieties make their appearance, such as the oak, firs, and several others common in the temperate zones. Near the equator the oak grows at an elevation of 9200 feet above the level of the sea, and never ce- scends lower than 5500 feet. It therefore follows that if the whole of the land within the tropics were to be elevated to 8000 H 98 feet all the tropical plants would disappear, as there would be only a temperate zone within the tropics; if, on the contrary, the land was depressed so as to be entirely below 3000 feet, or say mean temperature 75°, there would be only the productions of the hot regions: therefore the oscillations of the land must considerably influence the width and parallelism of the zones. In the former there would be no tropical band on dry land, and in the latter case it would be much augmented ; consequently they can never be definitely marked, or permanently preserve their parallelism. When we compare the productions of the southern hemisphere with the north, in corresponding zones of equal mean tempe- rature, we find a great difference. Among the tallest of living trees the Norfolk Island pine is found in south latitude 30°, but is not known in the north temperate zone. ‘Tree ferns, which require abundance of moisture, as well as equalization of heat, are found in Van Diemen’s Land and New Zealand in south latitude 45°: there are none in a corresponding latitude in the northern hemisphere. The distribution of plants cannot therefore be explained solely by the influence of climate, for it frequently happens that similar climates are found in different parts of the globe without identity of productions. In ascending from the vegetable to the animal world, and from one rank of animal existence te another, the most admirable order is manifest. Each description of zoophyte has its place of residence determined by the temperature and nourishment required for its support. The zones of depth below the level of the sea may be governed by a law similar to those above. Professor EK. Forbes, in his admirable observations on the Mollusca and Radiata of the Aigean Sea, states, “It was found to be a law, that the extent of the range of a species in depth is correspondent with the extent of its geographical distribution. On the other hand, species having avery limited range in depth were found to be either peculiar Mediterranean forms, or such as are extremely rare in the Aigean, but abundant in more northern seas. The Testacea of the Atgean are for the most part dwarfs, as compared with their analogues in the ocean, and the number of Medusz and Zoophytes are comparatively small. Below the fourth region in depth the number of animals dimi- 39 nishes as we descend, until, in the lowest part of the eighth region, the number of Testacea was found to be only eight, in- dicating a zero in the distribution of animal life at probably about 300 fathoms. “In the upper regions the more southern forms prevailed, whilst those of the lower zones presented a northern character, indicating a probable law, that in the distribution of marine animals regions of depth are equivalent to parallels of latitude. “Any oscillations of level, however slight, would produce alternations of strata containing distinct groups of organic beings with others void of such; and partial alternations of marine and freshwater beds would be formed, a phenomenon now in progress on the coasts of Asia Minor. All this would occur without con- vulsions or violent catastrophes of any kind. Changes of level, however slight, might cause the extinction of whole genera of animals and plants, of which only such as hard parts would be preserved. Were the present sea-bottom of the Aigean to be upheaved, whole classes of animals would disappear and leave not a trace behind to assure the future geologist of their having existed *.” With respect to fishes, it is probable that every basin of the ocean has its particular tribes; while indeed the regions which some inhabit are well known. The most remarkable species of fish are met with in the torrid zone and its vicinity. Here the lizard tribe, under the various names of crocodiles, gavials, alligators, and bavilla, attain to an immense growth; but each variety, although within the same zone, is confined to particular regions, as the crocodile of the Nile and the alligator of the Orinoco. When we consider terrestrial animals, but more especially those that are wild, we may divide the earth into a number of zoological regions or provinces, each of which, in the same in- dividual zone, is the residence of a distinct set. The first of these provinces, if we commence from the north, is the arctic region, which contains the white bear, the rein deer, the arctic fox, and other tribes common to both of the great continents. The northern temperate zone is divided by the ocean into two great districts. The same tribes are found to be spread from * Athenzum, No. 830. H 2 100 the western to the eastern parts of the old continent; but the quadrupeds which inhabit the temperate climate of America are peculiar races. The equatorial region contains three extensive tracts widely separated from each other by sea: each of the three tracts has a distinct nation ef quadrupeds. The large re- gion of Australia forms another zoological province, in which are contained many indigenous tribes of a very singular descrip- tion; and lastly, the southern extremities of America and Africa are each distinguished by the possession of peculiar races. Of these several provinces into which the animal world admits _ of division, none has so remarkable a stock of animals as Australia. It possesses several entire genera of quadrupeds which have been discovered in no other part of the world. One remarkable tribe is the Marsupial, which term comprises such as produce their young in an immature state, and keep them for a time attached to their bodies, chiefly in abdominal bags, given them by nature for that purpose. The opossum is peculiar to the southern hemi- sphere, and is very common in the lofty forests of America. We behold in every region striking instances of the structure of animals being fitted to the general nature of the country in which they reside. If we take a general view of the zones of equal temperature, both above and below the level of the sea, and consider that each has its peculiar vegetation, and again, that each zone is furnished with different groups of animals adapted to its temperature and general production, we can easily conceive that a very slight oscillation of land and sea would cause the extinction of whole genera of animals and plants, and that those bands of variable temperature, from the equator to the poles, can never be ex- pected to be parallel to the equator, but always to present great undulations according to the relative position and height of the dry land and the bottom of the sea. Therefore,in tracing the general effects of the northerly movement of the surfaces, and comparing the effects with existing nature, we must take all the above questions on the modifying causes of temperature and variable distribution of vegetables and animals into conside- ration, and not be limited to the mathematical zones of geo- graphy. In closing this chapter, we may note, that various calculations 101 have been made with the view of ascertaining the mean depth of the sea; this is a mathematical refinement which cannot be supported by physics. We may as well attempt to find the mean height of the dry land above the level of the sea by cen- trifugal forces, &c.* However, our present question is that of observation, and need not be mixed with geometrical analysis ; and we recommend the reader to refer to actual facts, and judge for himself. CHAPTER XV. ON THE POSITIONS, UNDULATIONS, CONTORTIONS AND FRACTURES OF THE SEDIMENTARY ROCKS. Tuat disturbing forces have acted on the sedimentary rocks during and after their formation, is abundantly proved by their general appearance in all partsof the world. We have shown that the surface of the dry land has been cleaved, fractured and dis- located, and that there is scarcely an area of a few square miles which does not bear marks of having been acted on by subter- ranean forces. Since this is the case with the fundamental cry- stalline base, it is reasonable to suppose that the sedimentary beds deposited on it would be similarly affected; not simply by the periodical and sudden effects of earthquakes, but by the quiet and insensible slow action of the magnetic currents, perpetually altering the plane of the beds by numerous undulations and different relative positions ; so that a series may commence to be deposited on a concave, half formed on a level plane, and completed on a convex surface ; sometimes receiving the elements on the one side, and again on the other, according to the nature, amount and continuity of the subterranean forces. Suppose, for instance, we find a series of rocks in the north- * Persons who have been led to suppose, by the established geometrical theory of the ‘ Principia,’ that at the equator centrifugal and centripetal forces are equal, and that the trade-winds sweep over the zone with great force always in one direction, &c., may probably be surprised when informed that such is not the case. 102 ern hemisphere, containing in the ascending order, first, beds with organic remains belonging to the south temperate zone ; another series of beds inclosing marine and terrestrial ani- mals corresponding to those of the tropics resting on them ; and again, beds of marine and freshwater shells alternating, similar to those now living in the northern hemisphere, com- pleting the series: such a formation would show that the beds must have undergone a considerable oscillation since the com- mencement of their deposition. The whole series, in moving from zone to zone, would be governed by the local nature of the base on which it rested, and would necessarily conform to all the changes which may periodically occur in the inferior bed. One of the most satisfactory results arrived at in the study of the sedimentary rocks, is the certainty that the subterranean movements of the solid crust of the globe, to which the deranged positions of the strata are owing, were not all of the same date, but that some mountain ridges and some lines and points of stratified rocks had been bent and disturbed before others were formed. Let us suppose a coal formation to be now forming near the mouth of the Rio de la Plata, and the movement en masse northward to be 20 seconds per annum, it would take 2200 years to arrive within the tropic of Capricorn; during this period there would be very considerable changes in the confi- guration of the land ; and when we consider the longitudinal ex- tent of the movement, say about 750 miles, we need not be sur- prised that the mass should happen to be much contorted and elevated or depressed a few thousand feet from its former rela- tive position. From the tropic of Capricorn to the equator the sedimentary mass may remain above the level of the sea and form the habitation of the organic beings confined to that part of the earth, whilst another mass of the same age may still remain under water. From the equator to the tropic of Cancer it may become again submerged below the level of the sea, and thus receive additional layers of sedimentary beds; on its emergence from the sea in the northern hemisphere, it would present an undulated compound, containing a different series of organic remains belonging to distinct zones, with one strong line of demarcation, showing the absence of the beds belonging 103 to the south tropical zone, arising from its being then above the sea level. It will, therefore, be observed, that although the sedi- mentary series of rocks are commonly described as if they were regularly built on each other in the following order, Cambrian, Silurian, Coal formation, Lias, Oolite and Chalk, with a series of beds called Tertiary, they are never found so complete in nature. It is true that the order of the beds is never found inverted, yet a great number are always absent, and their re- spective development varies considerably in different localities. England contains almost all the series from the south frigid to the north temperate, but not piled on one another, as described in the usual geological sections, but overlapping at the edges at different extremities of each other, thus showing that although some parts were constantly under the sea receiving new deposits, they were not always the same, but alternately changing accord- ing to circumstances. By reading some geological works it may be supposed that the earth was once actually covered by all the variety of beds, like the concentric coats of an onion; but such an idea is very erroneous, because it is abundantly evident that the depositions were extremely local. _In order to give a more general idea, and comprehend the re- lations of superposition of the sedimentary rocks, as actually observed in the different zones from south to north, and to show that although the order is never inverted, the beds are often wanting, and seldom seen in their complete numerical order, we shall enumerate the series in the following manner :— Deposits. Contents. Geological names. 1. South frigid Trilobite, Orthocera- Cambrian and Si- zone. tite, &c. lurian. 2. South tem- Terebratula, Producta, The great coal for- perate. Encrinite, Spirifera, mation. &e. 8. South tropic. | Ammonites, Belemnite, Oolite. Gryphite, &c. 4. North tropic. BKchinus, Fusus, Pec- Chalk and clay. ten, &c. 1. Commencing our examination south in Patagonia, we find, by a transverse section from Rio Santa Cruz to the base of the Cordilleras, and another on the Rio Negro, that the whole sedi- 104 mentary series is of recent origin, and irregularly covering the primary rocks. The shells and corals of the lowest deposit are those which belong to the bordering sea. Scattered over the whole, and at various heights above the sea, from 1300 feet downwards, are recent shells of littoral species of the neighbour- ing coast, so that every part of the surface seems once to have been a shore, thus indicating a very gradual elevation. In this part of the globe we only find irregular recent beds of No. 1. The fossils obtained by Mr. Darwin from the recent formations of Tierra del Fuego and Falkland islands can hardly be distin- guished from species found in the Silurian rocks of England*. 2. The south temperate.—In the Brazils we find isolated masses of No. 1, with occasionally thin beds of No. 2. In Au- stralia, on the eastern coast, a similar series has been observed. 3. Near the equator, according to a section made by the writer, embracing the three Cordilleras, the following numbers will re- present the variation in the ascending order :— , 3 3 3 3 CARS a os eae 3 oii apd Sphaoa we Primary ..... 0. /.01x01). 00M eoersotnD This enumeration furnishes an easy method of indicating the equivalent beds, apart from their relativé ages in the different zones, and also the local suppression of some of the series. 4. North tropic.—The sedimentary rocks of this zone are similar to the preceding, but much more developed. In the north temperate zone these rocks have been well investigated ; and we find in the United States and Europe the following order:— 3.4 4 Nedimentaryas< 2un3- qos 2 4 4°23 1 dk 02. dy EOS 2S Se Prumary, 2.7! oo: 0.0. 0. O-¢ Gr O20 0 YOR Bares Consequently it follows, that although No. 4 (chalk) covers No. 3 (oolite), the latter is not always formed: either of the series may be deposited immediately on the primary base; and it is necessary to obtain other indications than No.3 to ascertain the existence of No.2 under it. However, we know that No. 3 can- * Darwin, Voyage of Beagle, p. 253. 105 not be found under No. 2, nor any other in the inverted order. A deposit may be of the same age and belonging to the same zone, that is, exactly equivalent to another, and yet differ both in lithological and zoological character, and thus cannot be deter- mined without the aid of the inferior and superior beds. During a late survey in Ireland the writer saw pits being sunk in No. 1 in search of No. 2 (coal) on the eastern side of the Wicklow mountains; although no fossil could be detected in No. 1 to prove that coal could not exist below, yet the structure of the beds, and their lamination, enclosing veins of quartz and pyrites, were sufficient to show, not only their contact with the primary base, but their actual transition: it was like cutting into the body of a tree in search of the bark. When the upper series of the sedimentary beds are much developed the lower are seldom found underneath, and vice versd ; it 1s essential to bear this fact in mind when making trials for coal below the Chalk, Oolite, &c., as a thick seam of coal could not exist, even had it been originally deposited in the spot, under such a pressure as would be produced by a complete set of the superincumbent series ; therefore those who have studied geology from theoretical sections must modify their ideas on this point. It is a very common observation in geological works, “ that we can, by the aid of geology, see as it were into the interior thirty miles or more; for Pallas had described, in the peninsula of Tauris, a series of parallel strata as regular as the leaves of a book, inclined at an angle of 45° to the horizon, and exposed in a continuous section eighty-six English miles long.” The above series is a laminated crystalline rock, and not sedimentary beds. In South America, we may see sections of such a series for up- wards of 300 miles in extent, in an east and west direction, exhibiting such inclined planes. To deduce the thickness of the earth’s crust by the planes of lamination, is like calculating the depth of a transverse section of a tree by the medullary rays instead of the concentric rings. The more recent deposits must necessarily be less contorted and fractured as a whole than those which are more ancient, on account of their being subject to less disturbances, and not so compact: the fractures and dislocations visible on the surface of any series of rocks would not afford a just estimate of the amount Ca 106 of disturbances to which that particular part of the earth’s sur- face has been subjected. Extensive ranges of country often have the beds of rock of which they are composed thrown into particular lines of direction. Such lines, when considered in the usual manner with reference to our general ideas of distance, appear of considerable length ; but when viewed, as they should be, in connexion with the whole superficies of our spheroid, a large proportion of them lose their apparent importance: many of them are then seen to be so short, that the cracks or eleva- tions of strata by which they are marked may readily be con- ceived to have been effected by comparatively small intensities of force. It is a want of due attention to the relative propor- tions of the radius of the earth to the height of mountains and the undulations of strata, which is probably the cause of such disturbances being considered as the result of forces so tremen- dous as those arising from an igneous nucleus and a broken shell. (See Plate XX.) Most gigantic and awful igneous forces are now commonly brought forward to account for disturbances which could be effected by an ordinary hydrostatic press con- nected with a subterranean sheet of water. The gradual northerly crystalline action of the Dartmoor gra- nite tilting the southern edges of the strata of North Devon has been ascribed to an igneous eruption. It is a singular fact that the sedimentary beds are principally tilted on the southern edges in Europe and America, indicating very forcibly the effects of a northerly action. When we minutely examine the faults in coal-fields, we have abundant proofs that they were not the effect of volcanic con- vulsions or earthquakes, but the result of a quiet, uniform ope- ration of nature. Movements, fractures and dislocations, of such order, regularity and extent as we find in the whole masses of rocks constituting the surface of the globe, require a correspond- ing, slow, regular and powerful acting cause, such as that which we find in the operations of terrestrial magnetism. Volcanoes and earthquakes are merely secondary forces, 2. e. the effects of the subterranean currents; therefore even the local and irregular effects from these actions must be classed under the same natu- ral operation as those above alluded to. It 1s anything but de- sirable to have constant recourse to great forces in explaining 107 geological phenomena, when the exertion of a comparatively feeble power will afford sufficient explanation. We very com- monly observe in coal works, when the workings happen to be very extensive, the lower beds swelling upwards, and sometimes the upper bulging downwards until they meet, without produ- cing a single crack; here we have contortions of solid rocks by a slow action, without those awful subterranean disturbances and igneous matter to soften rocks, which some geologists are so fond of contemplating. The mere elevation and contortion ~ of mountain masses can be produced by a slow force as well as by other means; and the examination of these upraised moun- tains shows that the effects could not be produced by one great and instantaneous action. Contortion requires that the rocks should be in a yielding state, and that the particles be capable of a certain movement among each other, so that in applying force no absolute fracture would occur. Were we to attempt to bend a bed of limestone by one instantaneous action, the proba- bility would be that it would immediately break; but if we gra- dually apply pressure, so slow as to afford time for the consti- tuent particles to adapt themselves to the change, the bed may be subjected to any degree of contortion without fractures while in situ; where it is always saturated with carbonic acid and the usual natural solvents. The volcanic forces are insignificant compared with the apparent feeble force of magnetism ; it is like the effect of a blow from a sledge on a sheet of ice on a pond, compared with those effects which would be produced by water if confined and connected with a hydrostatic press; the former would exhibit a great break in one individual spot, but the latter would fracture and bend the ice throughout by a slow and in- sensible action. The disturbances thus produced on the ice would be greater-than those observed in the crust of the earth, when viewed in their relative proportions. When we consider that rocks have been liable to be contorted from the time they were in a state of mud to their consolidated state, we can easily conceive why they should present such bends as we now findin them. ‘The extent to which the particles of various rocks, saturated with water as they always are in na- ture, may be compelled to move among each other by great pressure, has never been sufficiently considered. Indeed rocks 108 have been viewed too much in the sense of dry, hard and inert, instead of active and moist masses: an absolute dry and compact rock would be a phenomenon in nature, i. e. an extraordinary exception to the usual natural production. It is exceedingly difficult to expel moisture from rocks, and when expelled the difference in weight is found very considerable. Limestones contain a great quantity of water, and are sometimes found at great depths very soft; and often, by means of the weight of the supermcumbent beds, force a great proportion of their soft parts imto the joints of the bounding beds. Some- times limestone beds and hornblende veins have been thus in- troduced between the planes of sedimentary beds. As this part of the subject has been anticipated by the observations made on the nature of the crystalline rocks, we need not extend them here; we shall conclude by stating that stratified rocks are not homogeneous inflexible dry and solid masses, on the contrary they are composed of numerous moist and pliable sheets, capable of extension and compression, and easily twisted and bent under pressure. We have already alluded to the effects of cleavage, 7. e. that all the sedimentary rocks are liable to be cleaved by the primary base*: this is particularly the case with coal, and which greatly facilitates the extraction ofthe coal-seams. Parallel to the strati- fication of the seam are, first, the partings; intersecting these, in a more or less vertical position, are the polar cleavages : these last separations are sometimes called backs or slines, or bright heads, from the coals separating at these cleavages with clean and highly polished surfaces, except when, as often happens, the complanatory lustre is covered with a rusty-looking scale, or with the well-known white sparry concretion, consisting for the most part of carbonate of lime, derived from the infiltration of the so- lutions of the bounding beds; besides these fissures, there are others passing nearly at right angles to the planes of cleavage, fractured divisions, and appropriately denominated cufters: so that by means of this compound system of natural series of lines, * Attempts have been made to distinguish sedimentary beds by the cleavage alone, but this is no guide, because any bed or compact soil even is liable to be cleaved by the primary in favourable localities. In New Grenada the soil is often found cleaved subsequently to the growth of the oldest trees. - : 109 the coal, under favourable circumstances, easily breaks down in _ parallelopipedal masses. Faults. In Chapter VIT., on Dislocations, &c., our observations were principally confined to horizontal and diagonal movements ; but in sedimentary or more or less horizontal beds, these kinds of disturbances are not so much felt as the vertical displacements called “ faults.” They are first produced by the splits and trans- verse fractures of the primary base, as already explained. The north and south lines are called main faults, and the east and west cross faults. When the strata rest on a semifluid base, such as beds of clay and moist carbonate of lime, the divisional planes disturb the uniformity of the pressure, consequently the isolated masses will gradually subside or elevate according to the angle in which they are separated. The most simple and fre- quent case of faults is represented in Plate X XI. Let us consider what would be the consequence of the oblique separations of the series of beds in Fig. 1, supposing they rested on a soft stratum. According to the laws of statics, the pressure will in- crease as the lower area of the masses becomes less than the upper, and vice versd: the weight divided by the area will give the amount of each, therefore the wedges will sink and the parts between them rise to restore the equilibrium of the pressure on the semifluid base, as illustrated in Fig. 2. The planes or joints, when they are found in contact, are often seen grooved and po- lished by the friction or the rubbing of one side against the other: and as the direction of the action must necessarily de- pend on local variations, the polished striz are not always pa- rallel, but commonly curved and irregular. Sometimes the beds are separated vertically upwards of 1000 feet, yet the masses of the uplifted and depressed strata do not present such irregu- larity on the surface ; the action haying been so extremely slow, that the upper parts have been modified and obliterated by at- mospheric and aqueous causes; during the displacement there- fore we only see the wreck of the elevated masses in the shape of sand, clay, &c., and the greater part of this washed away. It has been supposed that even these “ faults” were the result of violent mechanical convulsions produced by volcances, but 110 such notions have arisen from the want of a more practical knowledge of the general appearance and order of the disturbed strata. Sometimes “ faults” are filled with clay and various other substances from the base below, or from the softer inter- stratified seams by means of the pressure; these clay veins are impermeable, and consequently the water percolating in each mass is retained by these natural dams, which is of great ad- vantage to the independent workings of coal districts. The coal on one side of a fault is often different from that on the other side; sometimes losing its bituminous quality and be- coming impregnated with other elements. Occasionally a per- fect transition may be observed from anthracite to bituminous coal, the modifying cause being from the former to the latter. Not only is the water separated by the “ faults,” but also the subterranean gases, the local accumulation of which is much influenced by the angular position of the “ faults”? and dip of the beds. This interesting question deserves a separate investi~ gation in connexion with the best mode of ventilation, or prac- tical means of neutralizing the disastrous effects of these dan- gerous elements, which the coal miner has to encounter: we shall leave it to those who may have the opportunity of making the necessary examination. CHAPTER XVI. GENERAL OBSERVATIONS. Ir we now take a general view of the effects of terrestrial mag- netism in combination with other secondary agencies really ex- isting, we find a sufficient natural cause to explain all the. cha- racteristic changes which have been observed in the earth’s con- dition, in the degree, combination and sequence which actually belong to them. Each of the phenomena, taken singly, is capa- ble of demonstration in all its details of circumstances by the operations of terrestrial magnetism in connexion with some special branch of natural science. First. We have ample proofs of the existence of the magnetic Uy 2 fluid enveloping our globe, and that it has two points of conver- gence, which we call poles; that this fluid has a motion from the south to the north pole, and has an influence on all matter, causing all bodies to fall towards the earth, which we call attrac- tion of gravitation, and also tends to cause bodies to arrange themselves in a meridional direction, called polarity, as shown by the magnetic needle ; and that the latter action tends to propel all matter northward ; me finally, that it acts both mechani- cally and chemically on all matter. Secondly. This northerly movement is observed in the ocean, which is found to carry all substances that happen to float in it from the south to the northern regions. Thirdly. The grain of the primary crystalline presents a polar structure in all parts of the world, thus showing the universality of the action. The modification in the transitions of the different rocks, the elongation, fractures and dislocations, show the gene- ral northerly movement of the whole surface. Fourthly. Volcanoes and earthquakes appear to be the effects of the chemical action and meridional force of the magnetic currents. Fifihly. The formation of mineral veins, their general cha- racter, order, and numerous dislocations prove the action of a polar force; the constant operation of which is essential to ac- count for the observed subterranean phenomena. Sixthly. This northerly movement co-exists with the forma- tion of our globe ; it is the increased density of the currents at the poles which is the cause of its oblate figure; and it perpetually changes the surface of the earth, by bringing the consolidated masses, as they are formed in the southern hemisphere and other parts of the globe, towards the north pole, and thus exposing them to the temperature of different zones; consequently we find the relics of the southern in the northern hemisphere, Such series of beds are never found in the south, nor is the order of the deposits ever seen inverted. ‘Therefore we have no need to invent strange hypotheses to account for the observed facts, but simply apply the natural operations of nature, 7. e. the prime mover of terrestrial physics—magnetism, to guide us in our geological researches. If, then, this power is so extensive, and embraces that effect 112 which we call gravitation, its operations are not confined to the surface of our globe, but must extend to the whole solar system ; and if all space is filled with the magnetic fluids of the different celestial bodies according to their respective magnitudes, their movements must be explained differently to the commonly re- ceived hypothesis ; because a resisting medium is incompatible with the Newtonian philosophy, and a perfect void is imdispen- sable to the assumed geometrical movements demonstrated in the ¢ Principia.’ CHAPTER XVII. UNIVERSAL MAGNETISM. Wirs regard to the absolute diameter of the terrestrial mag- netic fluid, there is no definite data by which we can ascertain it; but from the apparent influence of the moon on the surface of the earth, together with her orbitual motion round the globe, we have reason to suppose that it extends to the orbit of the moon. Within the tropics we have striking evidences of the influence the changes of the moon have on the growth of vege- tation. From the new moon to the full there is a very intense action of the sap, accompanied by a great evolution of hydrogen from the leaves; and so strongly saturated are the trees during these periods throughout the year, that if cut and used for any purpose they would become rotten and useless in the course of a very few months. During the latter period of the change, viz. from the full to the new moon, there is a temporary sus- pension in the action of the sap, the woody substance becomes consolidated and is rendered fit for cutting. So much is this the case, that we find it rigidly attended to, from the making of a common fence to that of the largest works. It does not follow, that if a tree should contain 100 rings that it is a hundred years old; because within the tropics there are monthly rings, formed by the expansion of the external part of the trunk during the rise of the sap, and not, as has been supposed, by a mechanical return of the superfluous sap from the branches downwards between the trunk and the bark. A bamboo of three 4 * 113 years’ growth contains about thirty-six knots; each shoots out monthly, like the extension of a telescope. ‘The central pith, or heart of the trees, varies from the centre according to the angle of the hill on which they grow, the roots being generally more extended from the trunk down the hill than they are on the upper side, and consequently feeding stronger: the transverse sections of the trees on such declivities exhibit elliptical rings, very wide on the side of the strong roots, and diminish to mere lmes on the opposite side, as shown in the following sketch. iS Z B GE That the moon has an influence on the ocean is a fact well known, although not such as is usually represented according to the established theory of the tides. It is said “ that the moon attracts the ocean; that is, when any part of the surface of the sea is turned towards the moon the water is drawn towards it, and raised into a tide, which falls again when the place is turned away from the moon. The water rises to the same extent on the side opposite the moon; so that there is always high water on the two opposite sides of the globe at the same time. Let A B C D represent the earth, and M the moon, and let the surface at B next the moon, and that at D, opposite, consist of water.” - ~aa= - A BY / N \ £. Hopkins, dal ae 2 ty ee ae , ol } on Wee 2 2h oe er pian Pine? ee asmpy pun ssraUG WLUOLG TYP TSYIOL IUTIOISALD FUYA JO ‘Ums6 10 obnawaa “UOTQOUTULD) Jizz \ tsnzyygypyin \ 1, i L- tt UY} NW tj Uff} WAY YW fi) VEN WY by / iia Yéfyh pall Yyy y YA . VA YM Sf /; MA, fr / 4// Y Vy y Wy / Mf / y y) Yi// Mf f JO UoQoolip poLUol VY], buamoys SALOYAS TUL Mf PUY 4 PUL, | | Yy, _£. Hopkins, del? S Lasure, With. << bs al UY —<—J_—_ \ ies \ A lh / il LAA / Za V. FE As) } ~ Ah Z HN, Oe sw ae SQ Ss Ce: Sopa? 6 OS ate rete keto’ pa oe bsp Sikes ibe we een «ve ea Se ee eee WE ty OT aa a Bsryoy sc Se) LNT GLINVYS AHL JO NOTLLISNVUL A JS. Bastre, lath. Te ae £. Hopkins, i ae jm FE OT *¢tv> i eG P2LIT7 >» H Sa” Dey The arrows tndtcate the dtrection and position of some of the richest chanards. ase, lth. SL, LE. Hopkins, dele \ , po es Mepetee rorthwara. The ‘bunches of ore’ comparatively deep Southward. The ‘bunches of ore’ approachiny the surtacr The arrows indicate the direction of the nretallijerows currents, J Bastre, (177 ed - peel 16. Plate 8. Fractares not marked lo avotd confustor of “ies, #. Hopkins, del JS. Baste, Lethe. Plate lo. BY \YTAFAVAVAVAVAVAVAVINAVAVAY AVATAVANIVAYAVAVA W i AVA AVA AVAYAYAYA"AVAVAY iy SANSA NAW WAU AYATAPA m\/\ oy Apparent’ “a AP UNO Wy | dislocation. VY Aa WAYAAAVAN SAYA ATAAYAYAY YAAANATAVAVAVANDVAVIVAVAVAVATAVAVAA VV AVAYATAVAVATAYACAVAAAAATAVAVATAATATAPA ACA Cross Course Cross Coarse Ob livse angle L. Hopkins, del& JS Bastre, lith. | are IN uu l HANA wt | | | | | | | | ——— Bammer ceelmeiannencltinn ai | ff via "Mia ny |) WITT | | Tr UN i | | j —$—=— | | | | | | ——— | i ih Mi iM ili {AAMNLU(( AI HN ce I wil i ait i | | Hy thie Ms awit : en i a oy ay i = | | | bl cM | Flies | . | { i é HH iy " tui aR Wes | 3 | ly i 5 GG se letiecrale eal anni wil iti a Hey ae i | 3 S ny LA A ec ce a | Mm CAA ats anata aut | [| | ih l Wilt | | i i\( in Maile i i Mi WTA | | tif Li (LHL ill TTT TRU AHA eee i | Lc Git | uae Hg | { nae | Ne cnt poof Wy Why M ‘} \ eld (tl \\ OT hh ‘ Wie | ohey A Hiqal\u aye } Haq euifeqay i | ul sa \ \ ‘ ile ill Ua tid |! (tl a it wel Weta WIM WE TR (Lf "hi nN ily ihn i f Coot MUU yee agg hilt { PPRTRAV RUN (LL doe ean HN peta ai | ——— \ MV AN HPP HNSTTNIAN GA LE P a ARI i Md Al Plan of a metalliferons, formation on the ANDES shewing the old E&W veins undergoing obliteration by anew Lamination of siliceous & E. Hopkins, del? wi: Bastre, uth. le at i ee Ce ee 30a, # gas wk IY TA SSIES NOY pn ANAT AAY AN pSDSSS aN AKAKARADAMAAA NMA Mice rrs eS = PAYAYAVATAYAYADTAVAAVA'Travava" AVAVANAYAVAVAY? ACTANAANANNIVA en AAAI AD cae / Meee ona, y INAS TN JS Basire, libyi. #. Hopkins, del’ avr we en —— J. Bastre, lath. WY YWWWVV-V-. 8, dele sina 747 1 poipoqusa Yyoor 7y9 fo 940d buamoys Mpuunigy ny U2 Yo. snosvop{IbL” U0 fo UuoXeY 4. Hopkin ——_—— to, tl a a a i ll Nl ll Wa UG PLONT Wha Yj Y, UW ‘VOLIUTU fo SOYIUNG 42047 YPM (WP T/ SUM YosouUr fo uorgisod avWoyaL FY7 AFOIPSUPP? 07 suUuorqooy f afi J. Bastre, £. Hopkins, adelt Section. Y Po ae Section. North. Mineral Veins tr a sTAnfled ADSEFEELA- o ee (VVV\ ey ee M NN NA NV KY iv ” i IFT MM L\ fi AVAVAVAYAVAYAY, MANNA “ eee tt STORK - won “ i) 1\ Plan. Parallelism of the bunches ti a crystalline rock . ———_ ————— = KKAKZ WN VATU (ANNANA ‘ KARAANAAY | WAY NA N iN \ M } SAAAKAVAANAAZ J. Baszre, lath. Plate 16. Lo ne y supposed Igneous Causes. A Real Section, or the exact appearance of a similar series, ir an E .W. i \ | H JS, Basire, ath, we e > | a C.) e ee ee LS ae oe ee ee! OU ee lee, ,.!hlCUrEODU.UCUCL El Ome - ee = ——— er Ff s,s - “— Intluenre of the tmpermeable Splits on the acwminatattornr of AMinerats. Fracture. 7 Will reer WI, poor Ground ty rUChe ground ‘Burches’ of Ore tm a vetn of Fracture conivicd bo one side of the Spits . Diagranr to tllwstrate the apparent ease of the accumiutation . LZ fopzins, del * ed ad Y Silver Vetns tr state. \ \ \ = Brane A C8 <— a — | | ZL. & WW. fracthares. = eet —————SSS—————EEEEeeeee = SS Magnetic SS S NI a ET N N Q un the slate containing S pyiites. | 2 | | | x j va = | i} | S | \I : | I | = | | = | 2 : is o A? Lioots Oa apse E. Hopkins, Aelé J. Bascre, Lith. GOLD MINES on the WW CORDILLERA: 7 Veins of Fractures tn Horn blendre Lorphyty. 4. Hophires, dele . J Bastre, liuh. ein amet a ir — a — Ser a 3 gudla AT 2Y202 PAAOLD ‘G' PYP ULOdy LOPD UDI TY? LDIU ; IPWUL SUOTAONLISGO 02 GUNILOTID LIZIULDID TYR 40 3 noononunibne yussoddo ay? qu ‘shot suas He DUP £0 UIPPIOLYOL OY? SPUISILAIL BA0QY PUT 1 ae ——— | l So eit = 3 i{ | oe 3 |i sry fo 090)G 0 U0 FIGISL OQ FOU. Gy nOM “WIS WYP JO UU07209 FY? FF STOUT DUA JO EOUUNS Hyp ULOLL “ALY Hees ear ree | L9LUMAL fO UDLTOUDA TUZ TEDOLZESTYPL OF AZYOULIZLD UNIYS SUCHFOTAPUR FY} QLOLQLIUD UaQQUYIp 74707 UOHLod on ees el OU} fO -0L2 UD BITFUL QOL fO SFFUBYIZYUT V STUISALADL VYILLD YTOIQ FUT gatypLLg FY? U0 Y—~“Banbuadhiia unig | DY $9 SAL PUT E. Hophins, acL© TOPral nas 0f mine lv of diferent hinds Of ie "FE UTECS. alii UI Vetis of track Ditty EZ s AND) g % VEVUASURATNEY TOS | Ty zZ ———————— | Xl77e NOY: SEMI, ~s Sy SSE | LPO Copper > i £ Hopkins, del? Fliattif. Tatas aes es Se ee Se Solum So Sh. he ee Sie ae ie Se SLO VLG) ef LO SC OU i Spice [Vein PLUG BA. "FAULE S IN COAL BEDS. Subsidence and Llevation of the separate parts according tothe angles of the Fanttes . | a | <—_— =< : semt—-flutd base. Soft clay bcas forced tnto the jours. ‘Dylees? E. Hopkir-s, aelt JS. Baszire, lt, DIAGRAMS ILLUSTRATING THE COMPOSITION OF FORCES. uniform forces UIUASOTNU m eeling at right angle. =e ax MEET Oe ae. een eames! a WIUFOTVIL formning an Arc. »>- >—9—-8—_ = eos ta Mgewtadr 4 } he variable force exhausted the tangential exhausted. langcenttal force . ee ee A diagrane to = rn the foree well wee E Wie compostitorn of forces not admit ! of a rectan- ie 4 Th &, fore’ of attraction vs | 2 : AS ee anetorm at equa b Se es aistamnce trom the centre: _tnecreasthg tnwaras. £. Hopkins, del © %, vl a Ca fst OR I Orn hothae 1, wy ee loner erate whe wraps ay eg i Tee 5 saat, Cot rte ght ye Aes = StS : Fels STO ey | = cat % a ay \ wh ae | ae — ie ines, Lae) Pa C Hen sae x rs EEE 0 ae Ves f ary me r | | ety | ee | Mit iy | i Pe ee hi 1 ee inh: LTT On the connexion of geology with terrest