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SCENERY OF SWITZERLAND. 
but detached ridges. Moreover even when a valley 
is continuous for many miles it is interrupted here 
and there by the cross folds. 
These considerations then seem to account for 
the two main directions of the Swiss valleys. 
I must add, however, that in Prof. Heim’s opinion 
the cross folds occur in other parts of the Earth’s 
surface; and such bosses as the Furca and the Ober 
Alp are merely the battle-grounds of different river 
systems, the lower levels being due to more rapid 
denudation. 
Cirques. 
In some cases valleys end in a steep amphi- 
theatre known as a “Cirque.” 
Cirques are characteristic - of calcareous districts. 
They occur especially where a permeable bed rests 
on an impervious substratum. Under such circum- 
stances a spring, in many cases intermittent, issues 
at the junction and gradually eats back into the 
upper stratum, forming at first a semicircular enclave, 
which becomes gradually elliptic, and as time passes 
on more and more elongated, but always with a 
steep terminal slope. In the Jura, cirques are numer- 
ous, and in many cases a marly bed supplies the 
impermeable stratum. 
