CLOUDS AND RIVERS, ICE AND GLACIERS. 



iir 



tacnment, arc compelled to move more 

 quick?}'. A.putt\s therefore exerted, tend- 

 ing to separate the lower from the upper 

 snow. For a lime this pull is resisted by the 

 cohesion of the neve ; but this at length 

 gives way, and a crack is formed exactly 

 across the line in which the pull is exerted. 

 In other words, crevasse is for fried at rig/it 

 angles to the line of tension. 



39. TRANSVERSE CREVASSES. 



262. Both on the neve' and on the glacier 

 the origin of the crevasses is the same. 

 Through some cause or other, the ice is 

 thrown into a state of strain, and as it can- 

 not stretch it breaks across the line of tension. 

 Take, for example, the ice-full of the Geant, 

 or of the Talefre, above which you know 

 the ^crevasses yawn terribly. Imagine the 

 neve and the glacier entirely peeled away, 

 so as to expose the surface over which they 

 move. From the Col du Geant we should 

 sue this surface falling gently to the place 

 uo\v occupied by the brow of the cascade. 

 Here the surface would fall steeply down to 

 the bed of the present Glacier du Ge'ant, 

 v/liera the slope would become gentle once 

 more. 



26-J. Think of the neve" moving over such 

 a sin face. It descends from the Col till it 

 reaches the brow just referred to, It crosses 

 the brow, and must bend down to keep upon 

 its bed. Realize clearly what must occur. 

 Tlie surface of the ne"ve is evidently thrown 

 iito a state of strain : it breaks and forms a 

 Crevasse. Each fresh portion of the ne*ve as 

 it passes the brow is similarly broken, and 

 thus a succession of crevasses is sent down 

 the fall. Between every two chasms is a 

 great transverse ridge. Through local strains 

 upon the fall those ridges are also frequently 

 broken across, towers of ice xtfracs being 

 the result. Down the fall both ii<iges and 

 se'racs are borne, the dislocation being aug- 

 mented during the descent. 



204. What must occur at the foot of the 

 fall? Here the slope suddenly lessens in 

 steepness. It is plain that the crevasses 

 must not only cease to open here, but that 

 they must in whole or in part close up. At 

 the summit of the fall, the bending was such 

 as to make the surf ace con vex ; at the bottom, 

 of the fall, the bending renders the surface 

 concave. In the one case we have strain, in 

 the other pressure. In the one case, therefore, 

 we have the opening, and in the other the 

 closing of crevasses. This reasoning corre- 

 sponds exactly with the facts of observation. 



263. Lay bare your arm end stretch it 

 straight. Make two ink dots half an inch or 

 an inch apart, exactly opposite the elbow. 

 Bend your arm, the dots approach each 

 other, and are finally brought together. Let 

 the two dots represent tiie two sides of a 

 crevasse at the bottom of an ice-fall ; the 

 bending of the arm resembles the bending of 

 the ice, and the closing up of the dots re- 

 sembles the closing of the fissures. 



266. The same remarks apply to various 

 portions of the Mer de Glace. At certain 



places the inclination changes from a gentler 

 to a steeper slope, and on crossing the brow 

 between both the glacier breaks its back. 

 Transverse crevasses are thus formed. There 

 as such a change of inclination opposite to the 

 Angle, and a still greater but similar change 

 at the head of the Glacier des Bois. The 

 consequence is that the Mer de Glace at the 

 former point is impassable, and at the latter 

 the rending and dislocation are such as we 

 have seen and described. Below the Angle, 

 and at the bottom of the Glacier des Bois, 

 the steepness relaxes, the crevasses heal up, 

 and the glacier becomes once more continu- 

 ous and compact. 



40. MARGINAL CREVASSES. 

 2G7. Supposing, then, that we had no 

 changes of inclination, should we have no 

 crevasses ? We should certainly have less of 

 them, but they would not wholly disappear. 

 For other circumstances exist to throw the 

 ice into a state of strain, and to determine its 

 fracture. The principal of these is the more 

 rapid movement of the centre of the glacier, 



268. Helped by the labors of an eminent 

 man, now dead, the late Mr. Wm. Hopkins, 

 of Cambridge, let us master the explanation 

 of this point together. But the pleasure of 

 mastering it would be enhanced if we could 

 see beforehand the perplexing and delusive 

 appearances accoun'-jd for by the explana- 

 tion. Could my wishes be followed out, I 

 would at this point of our researches carry 

 you off with me to Basel, thence to Thun, 

 thence to Interlaken, thence lo Grindelwald, 

 where you would rind yourself in the actuat 

 presence of the Wetteihorn arid the Eiger, 

 with all the greatest peaks of the Bernese 

 Oberland, the Finsteraaihorn, the Schreck-r 

 horn, the Mouch, the Jungfrau, at hand. 

 At Grindelwald, as we have already learned, 

 there are two well known glaciers theObe? 

 Grindelwald and the Unter Grindelwald gla- 

 ciers on tlu latter of which our observa- 

 tions should commence. 



269. Dropping down from the village tQ 

 the bottom of the valley, we should breast 

 the opposite mountain, and with the 'great 

 limestone precipices of the Wetterhorn to 

 our left, we should get upon a path which 

 commands a view of the glacier. Here we 

 should see beautiful examples of the opening 

 of crevasses at the summit of a brow, and 

 their closing at the bottom. But the chief 

 point of interest would be the crevasses 

 formed at the side of this glacier the mar- 

 ginal crevasses, as they may be called. 



270. We should find the side copiously fis^ 

 sured, even at those places where the centre 

 is compact ; and we should particularly no- 

 tice that the lissures would neither run in 

 the direction of the glacier nor straight 

 across it, but that they would be oblique to it, 

 inclosing an angle of about 45 degrees with 

 the sides. Starling from the side of the gla- 

 cier the crevasses Avould be seen to point up- 

 ward ; that is to say, the ends of the fis- 

 sures abutting against the bounding moun- 

 tain would appear to be drrjgtd down. Were 



