202 
SCENERY OF SWITZERLAND. 
less continuous terrace above the new course. Such 
old river terraces may be seen in most valleys; often 
indeed several, one above another. The upper ter- 
races being generally cut in the rock, the lower ones 
in river deposits or fallen debris. 
It has been sometimes supposed that these ter- 
races indicate a greater volume of water in ancient 
times, sufficient indeed to fill up the whole valley to 
that depth. It must be remembered, however, that 
the terrace was formed before the lower part of the 
valley was excavated. 
54 is a section across the valley of the Ticino, 
a short distance below Airolo. It shows two high 
