ILLUSTRATIONS.
The Mer de Glace.—Showing the Cleft Station at Trélaporte, the Echelets, the Tacul, the Périades, and the Grand Jorasse.Frontispiece
Fig.Page
1. Ice Minaret14 2. Diagram of an angular reflector16 3, 4. Boats' sails inverted by Atmospheric Refraction35 5. Wave-like forms on the Mer de Glace43 6. Glacier Table44 7. Tributaries of the Mer de Glace53 8. Magnetic Boulder of the Riffelhorn143 9, 10, 11, 12. Luminous Trees projected against the sky at sunrise180, 181 13. Snow on the Pines201 14, 15. Snow Crystals214 16. Chasing produced by waves233 17. Diagram explanatory of Interference234 18. Interference Spectra, produced by DiffractionTo face 235 19. Moraines of the Mer de Glace" 264 20. Typical section of a glacier Table266 21. Locus of the Point of Maximum Motion286 22. Inclinations of ice cascade of the Glacier des Bois313 23. Inclinations of Mer de Glace above l'Angle314 24. Fantastic Mass of ice316 25. Diagram explanatory of the mechanical origin of Crevasses318 26. Diagram showing the line of Greatest Strain319 27a, b. Section and Plan of a portion of the Lower Grindelwald Glacier322 28. Diagram illustrating the crevassing of Convex Sides of glacier323 29. Diagram illustrating test of viscosity326 30, 31, 32, 33. Moulds used in experiments with ice346-348 34. Liquid Flowers in lake ice355 35. Dirt-bands of the Mer de Glace, as seen from a point near the FlégèreTo face 367 36. Ditto, as seen from les Charmoz" 368 37. Ditto, as seen from the Cleft Station, Trélaporte" 369 38. Plan of Dirt-bands taken from Johnson's 'Physical Atlas'374 39. Veined Structure on the walls of crevasses381 40. Figure explanatory of the Marginal Structure383 41. Plan of part of ice-fall, and of glacier below it (Glacier of the Rhone)386 42. Section of ditto386 43. Figure explanatory of Longitudinal Structure388 44. Structure and bedding on the Great Aletsch Glacier391 45, 46. Structure and Stratification on the Furgge glacier394 47. Diagram illustrating Differential Motion395 48, 49. Diagrams explanatory of the formation of Ripples400, 403 50, 51. Appearance of a prism of ice partially liquefied by Pressure.410 52, 53. Figures illustrative of compression and liquefaction of ice.411 54, 55. Sections of White Ice-seams414 56, 57. Variations in the Dip of the Veined Structure414, 415 58. Section of three glacier Crumples416 59. Wall of a crevasse, with incipient crumpling416 60. Plan of a Stream on the Glacier du Géant418 61. Plan of a Seam of White Ice on ditto418
PART I.
CHIEFLY NARRATIVE.
Ages are your days,
Ye grand expressors of the present tense
And types of permanence;
Firm ensigns of the fatal Being
Amid these coward shapes of joy and grief
That will not bide the seeing.
Hither we bring
Our insect miseries to the rocks,
And the whole flight with pestering wing
Vanish and end their murmuring,
Vanish beside these dedicated blocks.
Emerson
GLACIERS OF THE ALPS.
INTRODUCTORY.
(1.)
In the autumn of 1854 I attended the meeting of the British Association at Liverpool; and, after it was over, availed myself of my position to make an excursion into North Wales. Guided by a friend who knew the country, I became acquainted with its chief beauties, and concluded the expedition by a visit to Bangor and the neighbouring slate quarries of Penrhyn.
From my boyhood I had been accustomed to handle slates; had seen them used as roofing materials, and had worked the usual amount of arithmetic upon them at school; but now, as I saw the rocks blasted, the broken masses removed to the sheds surrounding the quarry, and there cloven into thin plates, a new interest was excited, and I could not help asking after the cause of this extraordinary property of cleavage. It sufficed to strike the point of an iron instrument into the edge of a plate of rock to cause the mass to yield and open, as wood opens in advance of a wedge driven into it. I walked round the quarry and observed that the planes of cleavage were everywhere parallel; the rock was capable of being split in one direction only, and this direction remained perfectly constant throughout the entire quarry.
CLEAVAGE OF SLATE ROCKS.
I was puzzled, and, on expressing my perplexity to my companion, he suggested that the cleavage was nothing more than the layers in which the rock had been originally deposited, and which, by some subsequent disturbance, had been set on end, like the strata of the sandstone rocks and chalk cliffs of Alum Bay. But though I was too ignorant to combat this notion successfully, it by no means satisfied me. I did not know that at the time of my visit this very question of slaty cleavage was exciting the greatest attention among English geologists, and I quitted the place with that feeling of intellectual discontent which, however unpleasant it may be for a time, is very useful as a stimulant, and perhaps as necessary to the true appreciation of knowledge as a healthy appetite is to the enjoyment of food.
On inquiry I found that the subject had been treated by three English writers, Professor Sedgwick, Mr. Daniel Sharpe, and Mr. Sorby. From Professor Sedgwick I learned that cleavage and stratification were things totally distinct from each other; that in many cases the strata could be observed with the cleavage passing through them at a high angle; and that this was the case throughout vast areas in North Wales and Cumberland. I read the lucid and important memoir of this eminent geologist with great interest: it placed the data of the problem before me, as far as they were then known, and I found myself, to some extent at least, in a condition to appreciate the value of a theoretic explanation.
Everybody has heard of the force of gravitation, and of that of cohesion; but there is a more subtle play of forces exerted by the molecules of bodies upon each other when these molecules possess sufficient freedom of action. In virtue of such forces, the ultimate particles of matter are enabled to build themselves up into those wondrous edifices which we call crystals. A diamond is a crystal self-erected from atoms of carbon; an amethyst is a crystal built up from particles