MODIFICATIONS OF DE SAUSSURE’S THEORY. 
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when he penned the passages which relate to their motion, is a mass of ice of small 
depth and considerable but uniform breadth sliding down a uniform valley, or pour- 
ing from a narrow valley into a wider one, as is the case with a vast majority of 
glaciers tolerably accessible, and which alone were visited at the time of publication 
of the first edition of the Voyages dans les Alpes. In all these cases the lateral 
resistance might easily be overlooked, and the popular comparison to one solid body 
sliding on another and lubricated by its own liquefaction might be accepted as a 
complete explanation ; as has even been done at a later period by those who have 
attempted to illustrate De Saussure’s theory by experiment, but who, like him, 
neglected the form and undulations of the bed in which it rests. 
§ 4. Modifications of De Saussure’s Theory. 
De Saussure and his immediate followers appear to have considered the crevasses 
which occur transversely in most glaciers, as the result of the inequalities of the beds 
down which they are constrained to move ; but other writers have imagined that the 
part which these crevasses perform in the phenomena of glacier motion is fundamental, 
and essential to the existence of the movement at all. Some writers have remarked 
that the fall of ice blocks over the precipice which often occurs near the lower end of 
glaciers, leaving the superior portions unsupported, allows them to advance to fill the 
position formerly occupied by the portion of the now fallen ice. But in this case it 
would appear that cause and effect are in some degree confounded. The ice about 
to be projected over the cliff must either advance towards its fall by its own gravity, 
or by the pressure of the parts behind. If its own gravity suffices, the same cause 
will urge the ice behind it to move similarly, whether the block in question fall or 
not ; and if it be the pressure from behind which shoves it on, then still more is the 
pressure of the entire glacier the cause of motion of the entire glacier, irrespective of 
the precipitation of its more advanced part. 
Thus, M. Martins’ theory of the progression of glaciers is, that the weight of the 
parts causes them to separate by fissures into wedge-shaped masses, without their 
sliding along the bottom ; that the fissures become filled with frozen snow, and that 
thus the glacier is perpetuated and extended year by year. “ Cette progression,” he 
says, “ n’est done ni un glissement ni un affaissernent difficiles a comprendre, puisque 
la glace doit adherer au sol, mais un demembrement successif*.” Besides other 
objections, it is now universally admitted that the glacier-proper does not grow by 
the consolidation of snow in its fissures. 
But setting aside the attempt to render the sliding motion of the entire glacier 
considered as a plane slab more easy, by considering the motions of the parts instead 
of the motion of the whole, we are led to notice the attempt to reconcile the sliding 
theory to recent observation, by ascribing to the crevasses of the glacier the import- 
ant office of enabling it to accommodate itself to the inequalities of its channel. 
* Martins sur les Glaciers de Spitzberg et de la Suisse. Bibl. Univ. Juillet 1840. 
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