forward has not been assumed to account for a particular phenomenon, but has been established by the facts, and proved by several years' experience, so that its application 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 practical operations of the mining engineer ; he may safely trust to the laws of terrestrial physics, and leave time to prov T e 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-ivork " and unprofitable undertakings, and thus tend to render this branch of our national wealth more certain and prosperous than it has hitherto been. February 1, 1844. On the Polarity of the Earth's Magnetism 3 CHAPTER II. The Identity of Magnetic and Galvanic Currents 15 CHAPTER III. On the Reduction of Metals by Electro-Magnetism or Galvanic Currents. 17 CHAPTER IV. On Heat produced by the Magnetic or Galvanic Fluid 23 CHAPTER V. Terrestrial Magnetism, or the Effects of the Positive and Negative Poles of the Globe on all Substances within the limits of their actions.-Cleavage Planes, &c 28 CHAPTER VI. On the General Character of the Crystalline Rocks called " Primary."-Granite, Gneiss, Schist, &c 35 CHAPTER VII. On the Order of the Splits, Fractures and Dislocations in the Primary Rocks, including the Superincumbent Sedimentary Masses.-Heaves, Slides, &c 43 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 Minerals in the Transverse Fractures.-Recapitulation 47 VI CONTENTS.
I t is a well-known fact to those who have traversed large areas of uncovered crystalline rocks, that they present a structure more or less vertical. In North America, Scotland, and Sweden the diversified edges of the crystalline series may he traced for many miles, presenting a north-easterly structural hearing. Where argillaceous sedimentary beds have been deposited on crystalline rocks, having the above vertical structure strongly developed, I have frequently observed the latter, by a slow chemical action, in the course of time obliterate the seams of deposition in the former, and cleave the beds in conformity to the angular position of the primary structure and the disposition of the crystals in the crystalline base. These cleavage-planes pass through mountains of undulated beds, and preserve throughout the various contorted seams, the geometrical parallelism of the structure of the parent rock below; thus plainly showing the effect of a polar crystallizing force, acting gradually and insensibly on the whole mass in one direction to an indefinite extent. Many thousand square miles of this vertical structure may be seen in South America, and in magnificent sections several thousand feet deep, exhibiting a great variety of colours, crystallization, and transitions of the primary series; as may be observed on reference to the sections exhibited to the Society, which have been carefully made from a very. laborious, survey carried, on during, many years, geologically, mineralogically, barometrically, and trigonometrically, this survey was not alone confined to the surface, but it comprehends the results of very extensive
The author described wide regions in several parts of the world as exhibiting in their geological structure the phænomena of successive vertical bands of schistose and crystalline rocks, parallel with each other, and having a meridional strike. This structural condition was illustrated by several extensive and highly finished sections, some of them traversing several hundred miles, made from the author's own observation in Panama, South America, Australia, and Ceylon. The section across the Andes, for instance, exhibited parallel bands of quartzites, porphyry, mica-schists, greenstone, granite, gneiss, hornblende schists, trachyte, crystalline limestone, talcose schists, and clay-slates, occurring in variable succession, with a N. and S. strike, and with an almost uniform vertical dip. In plains and other places where the laminated structure has not been disturbed by local causes, the cleavage planes were shown to be more or less vertical; but sometimes in high ridges with precipitous flanks the bands and laminæ of rocks drop on both sides, from want of lateral support, thus giving the appearance of a radial or fanshaped structure. Here and there on the edges of these laminated rocks rest horizontal sedimentary deposits; and it was pointed out that many of these exhibited at the point of contact with the older rocks evidence of their undergoing the process of vertical cleavage or lamination ; the lines of stratification becoming gradually obliterated. Even compact mud and soil lying on the edges of the schistose rocks have been observed by the author to be subject (under certain conditions) to cleavage and interlamination with calcareous and siliceous matter. Mr. E. Hopkins maintained that in all parts of the world the old crystalline or “primary” rocks exhibit (with local exceptions, insignificant when compared with the whole) a uniform vertical cleavage or foliation, with a north and south direction ; and that the rocks in those countries, like Australia, part of India, Siberia, South America, Central America, and California, which preserve this meridional uniformity, are productive of gold, platina, silver, and precious stones on the decomposed edges of the schists ; whilst those regions which have been disturbed or bent from their normal position are more or less productive in masses of the ordinary minerals, and are comparatively barren of the precious products. In speaking of the meridional structure, Mr. Hopkins alludes to the N.E. variation of the cleavageplanes in the northern hemisphere, more especially in the United States and Europe; but, nevertheless, he believes that the general uniformity approximates more nearly to the true meridian than the magnetic meridian does. The author observed also that, from his acquaintance during numerous mining operations with the deep-seated rock-masses of the Andes and elsewhere, he was convinced that the great base below was more or less granitic strongly saturated with mineral waters, and that it passed upwards by insensible gradations from a crystalline heterogeneous compound to a laminated rock (as gneiss), and still higher up to schists in vertical planes ; the peculiar varieties of the higher rocks being dependent on the mineral character of the “parent rock” below; the schistose rocks forming, in short, the external terminations of the great universal crystalline base. Mr. E. Hopkins referred to some important remarks on parallel lamination of nearly vertical rocks and on cleavage, made indeendently by Humboldt*, M'Culloch† Sedgwick‡, and De la Beche§ and, leaving for further consideration the question as to how the lamination and cleavage of rocks were brought about, he concluded by recommending the study of the primary rocks, with their various transitions and foliations, to the special notice of geologists, as being of extreme interest, and likely to throw great light on several important points in geological science.
With this communication, the author laid before the Society, and explained, a geological section of this south-eastern portion of Australia, extending from the Gleneig River, on the west, to beyond Mount Kosciusko, in the Australian Alps, on the east. This section exhibited the structure of this region as formed of great parallel bands of schistose and granitic rocks, having a north and south bearing and a vertical position. Along the line of section first appear the limestone-beds of the Gleneig Valley, resting on the foot of Mount William, in the Grampians, which consists of granite, capped by sandstone formed of the reconsolidated decomposed granite. Mount Cole, in the Pyrenees, next in order, consists of hornblendic schists. The Valley of the Loddon and Forest Creek are on the edges of the great gold band of argillaceous schists, interlaminated with auriferous quartz. These schists constitute the author's “great auriferous band,” extending north and south, from the south of Ballarat to the north of Bendigo and Korong. The granite of Mount Alexander succeeds; then the auriferous argillaceous band of the Campaspe Valley and the M'Ivor. This is the “M'Ivor auriferous band.” Granite, then the “Goulburn auriferous band,” the granite of Violet Town, and the “Ovens River auriferous band,” succeed in order to the eastward, and then the great granitic bands of the Australian Alps, occasionally interlaminated with clay-slate, &c.
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