206 
SCENERY OF SWITZERLAND. 
can travel much in Switzerland without seeing the 
great precautions taken to confine the rivers within 
certain limits. In fact, what we call the river bed, 
is rather the low-water channel, and the whole bottom 
of the valley would, but for these precautions, be 
covered during any considerable flood. Egypt itself 
is the river bed of the Nile during the autumn flood. 
Giants’ Caldrons. 
These are more or less circular cavities, often 
somewhat raised in the centre. They sometimes 
attain a considerable size — as much as 8 metres in 
diameter and 5 in depth. There is a very fine group 
at Lucerne, where they are known as the “ Jardin du 
Glacier.” They have been excavated in the rock by 
blocks of harder stone being whirled round by the 
action of water. Some of them no doubt, and cer- 
tainly those at Lucerne, were formed under glaciers, 
at the foot perhaps of a “moulin,” but I believe that 
as a rule they were formed in streams.* Several 
have recently been discovered at the Maloja; there 
are some fine specimens also near Servoz in the 
valley of the Arve. Renevier points out that such 
caldrons can be seen actually in process of formation 
in some of the existing rivers, as, for instance, near 
* Favre, Reck. Geol., vol. I. 
