For example, the dotted lines upon the map indicate the motion of the transporting medium. On ascending the valley of the Rhône to A, the diminutive representative of the ancient glacier is still found in existence, and is at work transporting boulders and moraines according to the law of ice-movement. Following down the valley from A, boulders from the head of the Rhône Valley are found distributed as far as B at Martigny, where the valley turns at right angles towards the north. It is evident that floating ice in a stream of water would by its momentum be carried to the left bank, so that if icebergs were the medium of transportation we should expect to find the boulders from the right-hand side of the Rhône Valley distributed towards the left end of the great valley of Switzerland--that is, in the direction of Geneva. But, instead, the boulders derived from C, D, and E, on the Bernese Oberland side, instead of crossing the valley at B, continue to keep on the right-hand side and are distributed over the main valley in the direction of the river Aar. As is to be expected also, the direct northward motion of the ice from B is stronger than the lateral movement to the right and left after it emerges from the mouth of the Rhône Valley, at F, and consequently it has pushed forwards in a straight line, so as to raise the Alpine boulders to a greater height upon the Jura Mountains at G than anywhere else, the upper limit of boulders at G being 1,500 feet higher than the limits at I or K on the left and right, points distant about one hundred miles from each other. All the boulders to the right of the line from B to G have been derived from the right side of the Rhône, while all the boulders to the left of that line have been derived from its left side. A boulder of talcose granite containing 61,000 French cubic feet, measuring about forty feet in one direction, came, according to Charpentier, from the point _n_, near the head of the Rhône Valley, and must have travelled one hundred and fifty miles to reach its present position. It scarcely needs to be added that the grooves and scratches upon the rocks over the floor of this great valley of Switzerland indicate a direction of the ice-movement corresponding to that implied in the distribution of boulders. Thus, at K upon the map referred to, Lyell reports that the abundant grooves and striæ upon the polished marble all trend down the valley of the Aar.[AU] [Footnote AU: Antiquity of Man, p. 305.]