240 
SCENERY OF SWITZERLAND. 
leys having been dammed up by the moraines of 
ancient glaciers. 
To this cause are due the Lake of Zurich (in 
part), the Lake of Halhvyl, of Sempach, several of 
the Italian lakes (Iseo, Orta), and many others. In 
fact, most of the valleys descending from the Alps 
have, or have had, a lake where they open on to 
the Plain. 
4. The fourth class of lakes were once even more 
numerous in Switzerland than at present. As cases 
of lakes due to rockfalls, I may mention the Torler 
See, near Zurich, and the Klon See in Glarus; among 
those due to river-cones the Sarnen See, and the 
lakes of the Upper Engadine; and as instances of 
lakes dammed back by glaciers the Lake of Tacul 
on the Mont Blanc range, and the Merjelen See, 
which is dammed back by the Aletsch glacier. In 
our own country the margins of such an ice-dammed 
lake form the celebrated “parallel roads of Glenroy.” 
5. Loop lakes occur along the course of many 
large rivers. The stream begins by winding in a 
loop which almost brings it back to the same point. 
The narrow neck is then cut through and the loop 
remains as a dead river channel, or “Mortlake.” 
Again, when an island is formed in mid-channel, one 
