THE CENTRAL PLAIN. 
33 
In fact, during the Miocene period, the country 
between the rising Alps and the Jura was a basin 
occupied sometimes by the Sea, sometimes by a 
great lake and then by the Sea again. The rivers 
from the Alps brought down boulders, gravel, and 
sand, gradually filling up the hollow, depositing the 
largest boulders at the foot of the mountains and 
carrying the finer materials further into the plain. 
The water escaped first perhaps by the Danube; 
there is some reason to believe that at one time it 
flowed by the valley of the Doubs to the Mediter- 
ranean, and lastly through Germany northwards, car- 
rying the finer materials to build up the plains of 
Belgium and Holland. 
Then came a period of cold — the Glacial period 
— when rivers of ice gradually descended from the 
mountains, filled up the valleys, and eventually 
covered the whole of the lower country with a great 
sheet of ice. 
The Mollasse consists of beds of sandstone, marl, 
and, especially as we approach the Alps, of a coarse 
gravel known as “Nagelflue,” which is often cemented 
so as to form a hard conglomerate. The pebbles 
are occasionally crushed, sometimes compressed, and 
••he sandstone often shows ripple marks, like those of 
nur present sea-shores. 
Scenery of Switzerland, //. 
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