might suit a purely spiritual essence, they are not congenial to flesh and blood, and you gladly escape from its magnificence to the sunshine of the world above. [Sidenote: BIRTH OF A CREVASSE.] From their numbers it might be inferred that the formation of crevasses is a thing of frequent occurrence and easy to observe; but in reality it is very rarely observed. Simond was a man of considerable experience upon the ice, but the first crevasse he ever saw formed was during the setting out of one of our lines, when a narrow rent opened beneath his feet, and propagated itself through the ice with loud cracking for a distance of 50 or 60 yards. Crevasses always commence in this way as mere narrow cracks, which open very slowly afterwards. I will here describe the only case of crevasse-forming which has come under my direct observation. On the 31st of July, 1857, Mr. Hirst and myself, having completed our day's work, were standing together upon the Glacier du Geant, when a loud dull sound, like that produced by a heavy blow, seemed to issue from the body of the ice underneath the spot on which we stood. This was succeeded by a series of sharp reports, which were heard sometimes above us, sometimes below us, sometimes apparently close under our feet, the intervals between the louder reports being filled by a low singing noise. We turned hither and thither as the direction of the sounds varied; for the glacier was evidently breaking beneath our feet, though we could discern no trace of rupture. For an hour the sounds continued without our being able to discover their source; this at length revealed itself by a rush of air-bubbles from one of the little pools upon the surface of the glacier, which was intersected by the newly-formed crevasse. We then traced it for some distance up and down, but hardly at any place was it sufficiently wide to permit the blade of my penknife to enter it. M. Agassiz has given an animated description of the terror of his guides upon a similar occasion, and there was an element of awe in our own feelings as we heard the evening stillness of the glacier thus disturbed. [Sidenote: MECHANICAL ORIGIN.] With regard to the mechanical origin of the crevasses the most vague and untenable notions had been entertained until Mr. Hopkins published his extremely valuable papers. To him, indeed, we are almost wholly indebted for our present knowledge of the subject, my own experiments upon this portion of the glacier-question being for the most part illustrations of the truth of his reasoning. To understand the fissures in their more complex aspects it is necessary that we should commence with their elements. I shall deal with the question in my own way, adhering, however, to the mechanical principles upon which Mr. Hopkins has based his exposition. [Illustration: Fig. 25. Diagram explanatory of the mechanical origin of Crevasses.]