240 ON GLACIERS IN GENERAL. 



glacier pushes forward its margin beyond the limit which it has 

 ever before reached (at least within the memory of man), tears 

 up the ground with its icy ploughshare, and shoves forward the 

 yielding turf in wrinkled folds, uprooting trees, moving vast 

 rocks, and scattering the walls of dwelling-houses in fragments 

 before its irresistible onward march.* 



The lower end of a glacier is usually steep ; sometimes 

 with a dome-shaped unbroken outline, more frequently broken 

 up by intersecting cracks into prismatic masses which the con- 

 tinued action of the sun and rain sharpen into pyramids, often 

 assuming (as in the Glacier of Bossons at Chamouni) grotesque 

 or beautiful forms. 



The united or crevassed condition of the glacier generally 

 depends almost entirely on the slope of its bed. If it inclines 

 rapidly, numerous transverse fissures are formed owing to the 

 imperfect yielding of the ice during its forced descent along its 

 uneven channel. These cracks often extend for hundreds of yards, 

 and may be hundreds of feet in depth ; but their greatest depth 

 is not accurately known, since they are rarely quite vertical. 

 In many cases, however, the crevasses are comparatively few in 

 number, and the glacier may be readily traversed in all direc- 

 tions. This is especially the case if a glacier of considerable 

 dimensions meet with any contraction in its course. The ice 

 is embayed and compressed, and its slope lessens, just as in the 

 case of a river when it nears a similar contraction preceding a 

 fall. Such level and generally traversable spaces may be found 

 about the middle regions of the Mer de Glace, the Lower Glacier 

 of Grindelwald, the Lower Glacier of the Aar, and in many other 

 cases. The last-named glacier is perhaps the most remarkably 

 even and accessible of any in Switzerland. The slope of its 

 surface is in many places only 3. The Pasterzen glacier in 

 Carinthia is even less inclined. It is in such portions of a 



Such a sudden and disastrous increase took place in many of the glaciers of 

 Switzerland and Savoy in 1818 (occasioning the catastrophe of the Val de Bagnes), 

 and in those of the Bergenstift in Norway ahout 1740. The retreat of a glacier far 

 within its old moraines is well exemplified in most of the glaciers of the latter 

 country, and especially in that of Nygaard. 



