1031 



GLACIERS. 



GLACIERS. 



foreign bodies, u sand and gravel, which the bird* iwallow ; them 

 bruise the grains of corn by the action of the muscles, and deprive 

 them of their viulity, when the gastric juice acts upon and dissolves 

 them. The pebbles thus perform the vicarious office of teeth. 



HunUr inferred that the action of the great digastric muscles of 

 the itomach in birds wat rotatory, and lays, " Although the motion 

 of the guzard i hardly visible, yet we may be made very sensible of 

 iU action by putting the ear to the side of a fowl while it is grinding 

 iU food, when the stones can be beard moving one upon another." 

 The pyloric or intestinal orifice of the gizzard is furnished with a 

 valve, which is of considerable sixe in those birds which swallow large 

 stones, as the ostrich ; it prevents them from passing into the intes- 

 tines, and it also keeps the food in the stomach until it bar undergone 

 a sufficient degree of trituration or mastication to fit it for nutrition. 



GLACIERS, a French word received into our language, and 

 which must not be confound'*! with Glacicre, which has a different 

 signification. 



The glaciers, as defined by Saussure, are those eternal masses of .ice 

 which are formed and remain in the open air in the valleys and on 

 the slopes of lofty mountains. 



In speaking of glaciers we generally refer to those of the Alps, as 

 being the best known, though there are many in other places. The 

 glaciers of the Alps have been frequently described by travellers, 

 geographers, and naturalists, but by none in so much detail as by 

 Ssussure and Oruner. 



If, says Saussure, a spectator could be placed at a sufficient height 

 above the Alps to embrace at one view those of Switzerland, Savoy, 

 and Dauphind, he would see a mass of mountains intersected by 

 numerous valleys, and composed of several parallel chains, the highest 

 in the middle, and the others decreasing gradually as they recede. 

 The central and highest chain would appear to him bristled with 

 craggy rocks, covered even in summer with snow and ice in nil those 

 places that are not absolutely vertical ; but on both sides of the chain 

 he would see deep and verdant valleys, well watered and covered with 

 villages. Examining still more in detail, he would remark that the 

 central range is composed of lofty penks and smaller chains, covered 

 with snow on their tops, but having all their slopes that are not very 

 much inclined covered with ice, while the intervals between them 

 form elevated valleys filled with immense masses of ice, extending 

 down into the deep and inhabited valleys which border on the great 

 chain. The chain nearest to the centre would present to the observer 

 the same phenomenon, but on a smaller scale, beyond which he would 

 see no more ice, nor even snow, aave here and there on some of the 

 more elevated summits. 



From what precedes, continues Saussure, I recognise two kinds of 

 glaciers, quite distinct from each other, and to which all their varieties 

 may be referred. The first are contained in the valleys more or less 

 deep, and which though at great elevations are still commanded on 

 all sides by mountains higher still ; while the second are not contained 

 in the valleys, but are spread out on the slopes of the higher peaks. 



The distinguishing features of the two kinds are the greater extent 

 nnil depth of the former, and the greater compactness of the mass; 

 but as these circumstances seem to depend on the situation of the 

 glaciers, as is proved by the insensible passage of the one kind into 

 tin- other in many localities, the distinction of Saussure seems to have 

 little foundation. 



The formation of the glacier;, whatever are their position and 

 appearance, is due to the great quantity of snow which falls in the 

 high and cold regions of the mountains, and which the beat of summer 

 can but partially thaw. When the slopes of the lofty peaks are very 

 rapid, the snow, being unable to rest upon them, slips down into the 

 valleys in the form of avalanches; and this being added to what falls 

 directly into the valleys, there is accumulated an enormous quantity 

 that becomes compressed by its own weight This snow is subse- 

 quently converted into a kind of ice by the following process : The 

 rains which occasionally fall, and the water resulting from the partial 

 melting of the snow in the warmer months, percolates the mass, 

 tccping it throughout ; and in this state, being seized by the cold of 

 the succeeding winter, it is consolidated into a glacier. It will how- 

 ever be easily conceived tl at the ice so formed is very different from 

 that found in pondi or lake* ; it has neither the hardness, the com- 

 pactness, the solidity, nor the transparency of the latter, but is, on 

 nlrary, porous and opaque. The water in filtering through the 

 mass not being able to drive out all the air lodged in the interstices, 

 this air, together with that which is liberated during the subsequi-ut 

 congelation, collects into bubbles of various forms and sizes, destroying 

 the transparency and cohesivencss of the mass. With regard to the 

 now which rest* on the slopes, it is evident that it will be subject to 

 the same effect of rain mid warmth as that iu the valleys, but, from 

 the very position in which it IK-s, the water in great port runs oft", or 

 is only retained towards the bottom of the slope, whence it results J 

 that the glaciers so situated are in general of much looser texture 

 than the glaciers of the valleys. It is only towards the bottom, M h.-n- 

 the water accumulates, that the ice of the former acquires a consist- 

 ence equal to that of the Utter. This solidity decreases as you ascend, 

 till towards the top there is nothing but snow. 



The surface of the glaciers depends entirely upon the ground on 

 which they rest. When the bottom is even, or but slightly inclined, 



the surface of the glacier, though rough and granulated, U also even, 

 presenting but few crevices, and these not wide ; but in proportion as 

 the bottom is inclined or rugged the surface is abrupted and uneven. 

 Ebel, who follows Saussure, says, that wherever the slope exceeds SO 

 or 40 degrees, the beds of ice break into fragments, which get dis- 

 placed, upheaved, and piled together in every variety of fantastic 

 form, and exhibit immense chasms many feet in breadth, and often 

 more than 100 feet deep. 



The splitting of the ice on a change of weather, or in consequence 

 of unequal pressure on an uneven bottom, shake* the very hills, and 

 produces a noise which, reverberated from the mountains, sounds like 

 thunder. The breadth and depth of the chasms thus occasioned vary 

 considerably according to circumstance*. Sometimes their dimensions 

 are rapidly increased, either from the slippling away of the lower mass 

 while the upper remains stationary, or in consequence of the erosion 

 of the water running down them from the thawing of the surface ; 

 and at other times they are suddenly closed up by the descent of the 

 upper portion against the lower, which is fixed. The ice at those 

 fissures down which the water flows freely is generally transparent, 

 and is observed to be of a greenish colour towards the top and bluish 

 towards the bottom. These clefU are frequently hidden by a 

 covering of snow, which render* them exceedingly dangerous. 



Along the anterior edge and lateral margins of some of the larger 

 glaciers there are masses of dubris accumulated into the form of long 

 dykes or parapets, which in the Tyrol are known by the name of 

 ' trockno muren,' and iu Savoy by that of ' moroiu,' which has iiMir 

 generally prevailed. In Iceland, where the glaciers are called ' jokul,' 

 the moraines are named ' jokii Isgiii rdc.' The formation of the moraines 

 is easily conceived. When the rocks bordering the glaciers are 

 themselves bare of snow or ice, in consequence of the rapidity of the 

 slope, and are schistose or stratified, they are easily disintegrated by 

 the alternate action of wet and frost, heat and cold, and the fragments 

 thus detached roll down to the lateral edges of the glacier, when- the 

 greater part is stopped, while some isolated blocks ore urged farther 

 towards the middle. The general inclination of the glacier and ito 

 progressive motion downwards also collect a quantity of these d<Sbris 

 along the anterior boundary of the ice-field, so that in some cases the 

 whole glacier is entirely surrounded by a moraine. Wherever the 

 mountain-slopes arc protected by a glacier of their own, or where the 

 rock is of compact indestructible granite, no moraine is formed. 

 Thus it happens that some glaciers have a moraine on each side, 

 others on one side only, and some none at all. Occasionally also a 

 moraine is found where none could have been formed, in which case 

 it is one that has been brought down from a higher station by the 

 motion of the glacier, as is evident from the nature of the I 

 These moraines sometimes attain a height of a hundred feet It is 

 observable however that when the glaciers have diminished in size, 

 the moraine is above the ice-field ; and when, on the contrary, the 

 glacier has increased the moraine is lower than the ice, and in some 

 cases the moraine and the ice ore on a level. 



M. Agassiz, of Geneva, in a paper on glaciers, moraines, and erratic 

 blocks, published in the ' Bibliotheque Universelle,' No. 24, 1837, h.-n 

 called attention to the existence of moraines at the height of > 

 hundred feet above the bottom of the superior Alpine valleys, li. i , 

 there are no longer any glaciers ; but in descending into the lower 

 valleys they are found in succession as high us twelve, fifteen, anil 

 eighteen hundred feet They may even be observed at two thousand 

 feet above the bed of the Rhone, in the neighbourhood of St Mauri'-", 

 in the Vallais, and can also be traced at a great height round the Lake 

 of Geneva : from this fact and other collateral circumstances M. Agassiz 

 concludes that at one time the glaciers covered the whole of the plains 

 of Switzerland to a height of 3300 feet above the level of the sea, or 

 2155 feet above the present surface of the Lake of Geneva, urn! 

 extended as far as the jura. To account for the existence of such 

 masses of ice he supposes the alternate cooling and heating of the 

 globe at distant but given periods. He appeals to fossil remains in 

 confirmation of his theory, and tries to explain the existence uf Ill-- 

 erratic blocks of the Jura by supposing them to be the transport rd 

 moraines of his immense glaciers. 



Besides the bordering moraines there are long and hi^h i-Mx. - 

 formed of fragments of rocks, boulders, sand, and earth, in the middle 

 of the glaciers, and at a considerable distance from the margins, to 

 which however they are generally parallel. These banks, which iu 

 the German cantons of Switzerland arc called ' guferlinien,' are some- 

 times numerous and high. Thus, in traversing the great ioe-field 

 above Montanvert, Saussure crossed four or five of them which wnv 

 30 or 40 feet high, an elevation due in port to the quantity of the 

 di'-lirin, and in part to the sinking of the surrounding ice, which thaws, 

 while that under the heap, sheltered from the sun, remain* inithau. I. 

 The glacier of Kosboden is said to exhibit the greatest number of 

 these ridges, and of the largest dimensions. The formation of those 

 banks is thus explained. The glacier progressively slipping down 

 upon the inclined bottom of the vulluy recedes from the sides, carry- 

 ing part of the lateral moraine along with and upon it. This r 

 often leaves a considerable apace, particularly in the wider valleys, 

 between the foot of the mountains and the edge of the glaciers, which 

 space, during the succeeding winter, becomes filled up with fresh 

 snow, which is converted into ice by the process already described 



