reams,
running approximately parallel to one another north-north-east, 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.

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.

[Illustration: Fig. 42.]

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 Isere from Albertville
to Grenoble, of the Rhone from its source to Martigny, of the Vorder
Rhine from its source to Chur, of the Inn from Landeck to Kufstein, of
the Enns from its source to near Admont, of the Danube from its source
to Vienna, and as just mentioned, of the Aar from Bern to Waldshut.
Hence also, whenever the Swiss rivers running east and west break into a
transverse valley, as the larger ones all do, and some more than once,
they invariably, whether originally running east or westwards, turn
towards the north.

But although we thus get a clue to the general structure of Switzerland,
the whole question is extremely complex, and the strata have been
crumpled and folded in the most complicated manner, sometimes completely
reversed, so that older rocks have been folded back on younger strata,
and even in some cases these folds again refolded. Moreover, the
denudation by aerial action, by glaciers, frosts, and rivers has removed
hundreds, or rather thousands, of feet of strata. In fact, the mountain
tops are not by any means the spots which have been most elevated, but
those which have been least denuded; and hence it is that so many of the
peaks stand at about the same altitude.

THE CONFLICTS AND ADVENTURES OF RIVERS

Our ancestors looked upon rivers as being in some sense alive, and in
fact in their "struggle for existence" they not only labour to adapt
their channel to their own requirements, but in many cases enter into
conflict with one another.

In the plain of Bengal, for instance, there are three great rivers, the
Brahmapootra coming from the north, the Ganges from the west, and the
Megna from the east, each of them with a number of tributary streams.
Mr. Fergusson[53] has given us a mos