GENERAL SUMMARY. 
253 
glaciers. These, however, are but the remnants of a 
much larger sea of ice which once covered almost 
the whole country. The glacier of the Rhone for 
instance descended the Valais, filled the Lake of 
Geneva, rose to, what is now, a height of 1350 metres 
on the Jura, and then dividing, sent one branch as 
far as Lyons, and a second along the Aar to Wald- 
shut. The Glacial period, however, was not con- 
tinuous, but interrupted by at least two periods of 
more genial climate. The mass of material brought 
down from the mountains partially filled the river 
valleys (which have not even yet been entirely re- 
excavated), formed great moraines, and is spread in 
thick, but irregular, masses over all the lower ground. 
The rivers of Switzerland run mainly in one of 
two directions, the first from south-west to north-east, 
or vice versa, following the strike and original folds 
of the strata, and the second at right angles to it. 
Many, indeed most, of the principal rivers, take first 
the one and then the other direction in different 
parts of their course. In some cases the rivers cut 
through mountain ranges, as for instance the Rhone 
between Martigny and the Lake of Geneva. This 
probably indicates that the river is older than the 
mountain range, and cut through it as it rose. 
The river system of Switzerland was, however, at 
