THE TICINO. 
235 
It is the lower part of the great fold of which the 
Alps form the upper arch, and must descend far 
below the sea level. 
The alluvial deposits are of great, but unknown 
depth; at Milan a boring was sunk for 162 metres 
without reaching the bottom,* nor do we know on 
what strata the alluvium rests. The lakes therefore 
may be compared with the fiords of Norway or of 
Scotland; they are ancient river valleys, which have 
sunk far below the sea level. 
It is probable that the plain of Lombardy was 
an arm of the sea during part of the Ice Age, for 
the manner in which the glacial deposits have been 
evenly spread over the plain can hardly be accounted 
for except by marine action. The hill of the Superga, 
near Turin, is miocene, bent into an anticlinal.** 
* Penck, Moj'ph. der Erdoherjldchc^ vol. ir. 
** Penck, Morphs der Erdoberflachcy vol. ii. 
