De Saussure devoted but little time to the subject of glacier-motion; and the absence of completeness in the statement of his views, arising no doubt from this cause, has given subsequent writers occasion to affix what I cannot help thinking a strained interpretation to the sliding theory. It is alleged that he regarded a glacier as a perfectly rigid body; that he considered it to be "a mass of ice of small depth, and considerable but uniform breadth, sliding down a uniform valley, or pouring from a narrow valley into a wider one."[B] The introduction "of the smallest flexibility or plasticity" is moreover emphatically denied to him.[C] It is by no means probable that the great author of the 'Voyages' would have subscribed to this "rigid" annotation. His theory, be it remembered, is to some extent _true_: the glacier moves over its bed in the manner supposed, and the rocks of Britain bear to this day the traces of these mighty sliders. De Saussure probably contented himself with a general statement of what he believed to be the substantial cause of the motion. He visited the Jardin, and saw the tributaries of the Mer de Glace turning round corners, welding themselves together, and afterwards moving through a sinuous trunk-valley; and it is scarcely credible that in the presence of such facts he would have denied all flexibility to the glacier. The statement that he regarded a glacier to be a mass of ice of uniform width, is moreover plainly inconsistent with the following description of the glacier of Mont Dolent: "Its most elevated plateau is a great circus, surrounded by high cliffs of granite, of pyramidal forms; thence the glacier descends through a gorge, in which _it is narrowed_; but after having passed the gorge, it _enlarges again_, spreading out like a fan. Thus it has on the whole the form of a sheaf tied in the middle and dilated at its two extremities."[D] [Sidenote: GLACIER OF MONT DOLENT.] Curiously enough this very glacier, and these very words, are selected by M. Rendu as illustrative of the plasticity of glaciers. "Nothing," he says, "shows better the extent to which a glacier moulds itself to its locality than the form of the glacier of Mont Dolent in the Valley of Ferret;" and he adds, in connexion with the same passage, these remarkable words:--"There is a multitude of facts which would seem to necessitate the belief that the substance of glaciers enjoys a kind of ductility which permits it to mould itself to the locality which it occupies, to grow thin, to swell, and to narrow itself like a soft paste."[E] FOOTNOTES: [A] 'Voyages,' Sec. 535. [B] James D. Forbes, 'Occasional Papers on the Theory of Glaciers,' 1859, p. 100. [C] "I adhere to the definition as excluding the introduction of the smallest flexibility or plasticity." 'Occ. Pap.,' p. 96. [D] 'Voyages,' tome ii. p. 290.