south, until it reaches St. Genix, where it falls into and adopts a transverse valley which properly belongs to the little river Guiers; it subsequently joins the Ain and finally falls into the Saône. If these valleys were attributed to their older occupiers we should therefore confine the name of the Rhone to the portion of its course from the Rhone glacier to Martigny. From Martigny it occupies successively the valleys of the Dranse, Guiers, Ain, and Saône. In fact, the Saône receives the Ain, the Ain the Guiers, the Guiers the Dranse, and the Dranse the Rhone. This is not a mere question of names, but also one of antiquity. The Saône, for instance, flowed past Lyons to the Mediterranean for ages before it was joined by the Rhone. In our nomenclature, however, the Rhone has swallowed up the others. This is the more curious because of the three great rivers which unite to form the lower Rhone, namely, the Saône, the Doubs, and the Rhone itself, the Saône brings for a large part of the year the greatest volume of water, and the Doubs has the longest course. Other similar cases might be mentioned. The Aar, for instance, is a somewhat larger river than the Rhine. But why should the rivers, after running Fix. 41. Diagram in illustration of Mountain structure. for a certain distance in the direction of the main axis, so often break away into lateral valleys? If the elevation of a chain of mountains be due to the causes suggested in p. 214, it is evident, though, so far as I am aware, stress has not hitherto been laid upon this, that the compression and consequent folding of the strata (Fig. 41) would not be in the direction A B only, but also at right angles to it, in the direction A C, though the amount of folding might be much greater in one direction than in the other. Thus in the case of Switzerland, while the main folds run southwest by north-east, there would be others at right angles to the main axis. The complex structure of the Swiss mountains may be partly due to the coexistence of these two directions of pressure at right angles to one another. The presence of a fold so originating would often divert the river to a course more or less nearly at right angles to its original direction. Switzerland, moreover, slopes northwards from the Alps, so that the lowest part of the great Swiss plain is that along the foot of the Jura. along the line from Yverdun to Neuchâtel. down the Zihl to Soleure, and then along the Aar to Waldshut the Upper Aar, the Emmen, the Wiggern, the Suhr, the Wynen, the lower Reuss, the Sihl, and the Limmat, besides several smaller streams, running approximately parallel to one another north-northeast, and at angles to the main axis of elevation, and all joining the Aar from the south, while on the north it does not receive a single contributary of any importance. Hence the main drainage runs On the south side of the Alps again we have the Dora Baltea, the Sesia, the Ticino, the Olonna, the Adda, the Adige, etc., all running south-south-east from the axis of elevation to the Po. Indeed, the general slope of Switzerland, being from the ridge of the Alps towards the north, it will be observed (Fig. 42) that almost all the large affluents of these rivers running in longitudinal valleys fall in on the south, as, for instance, those of the Isère from Albertville to Grenoble, of the Rhone from its source to Martigny, of the Vorder Rhine from its source |