some parts beds of sand and gravel were
spread out; in others, the solid rock had been worn into a broad
channel, which in one spot was about 40 yards in breadth and 8 feet
deep. It is self-evident that a person following up the course of a
stream will always ascend at a greater or less inclination. Mr. Gill
therefore, was much astonished when walking up the bed of this ancient
river, to find himself suddenly going downhill. He imagined that the
downward slope had a fall of about 40 or 50 feet perpendicular. We here
have unequivocal evidence that a ridge had been uplifted right across
the old bed of a stream. From the moment the river course was thus
arched, the water must necessarily have been thrown back, and a new
channel formed. From that moment also the neighbouring plain must have
lost its fertilising stream, and become a desert."[52]

The strata, moreover, often--indeed generally, as we have seen, for
instance, in the case of Switzerland--bear evidence of most violent
contortions, and even where the convulsions were less extreme, the
valleys thus resulting are sometimes complicated by the existence of
older valleys formed under previous conditions.

In the Alps then the present configuration of the surface is mainly the
result of denudation. If we look at a map of Switzerland we can trace
but little relation between the river courses and the mountain chains.

[Illustration: Fig. 40.--Sketch Map of the Swiss Rivers.]

The rivers, as a rule (Fig. 40), run either S.E. by N.W., or, at right
angles to this, N.E. and S.W. The Alps themselves follow a somewhat
curved line from the Maritime Alps, commencing with the islands of
Hyeres, by Briancon, Martigny, the Valais, Urseren Thal, Vorder Rhein,
Innsbruck, Radstadt, and Rottenmann to the Danube, a little below
Vienna,--at first nearly north and south, but gradually curving round
until it becomes S.W. by N.E.

The central mountains are mainly composed of Gneiss, Granite, and
crystalline Schists: the line of junction between these rocks and the
secondary and tertiary strata on the north, runs, speaking roughly, from
Hyeres to Grenoble, and then by Albertville, Sion, Chur, Inns, bruck,
Radstadt, and Hieflau, towards Vienna. It is followed (in some part of
their course) by the Isere, the Rhone, the Rhine, the Inn, and the Enns.
One of the great folds shortly described in the preceding chapter runs
up the Isere, along the Chamouni Valley, up the Rhone, through the
Urse