l6o SCENERY OF SWITZERLAND. 
crosses a longitudinal valley, known as the Urbach- 
thal (see ante, p. 152) on the west, the Gadmen- 
thal on the east. In both cases the lateral valleys 
are at a higher level than that of the Aar, following 
the general rule that transverse valleys are e.xcavated 
more rapidly than longitudinal, and the result is in 
each case a sharp rise from the Aar valley, that of 
the Urbach being the steeper of the two. 
Below Innertkirchen the valley of the Aar is in- 
terrupted by a ridge of Jurassic rock, known as the 
Kirchet, above which it has been supposed that the 
river once formed a lake in the depression known as 
“Hasli-im Grund.” Of this, however, there is no 
direct evidence, and it is possible that the river cut 
through the ridge as it rose. Studer* was disposed 
to regard the depression as due to an earthquake. 
In fact, however, it simply follows the normal slope 
of the river. The Aar has cut for itself a magnificent 
gorge, 300 to 400 feet deep, one of the longest and 
deepest in Switzerland. At both ends the rocks are 
much glaciated. 
Near the upper end is a water-worn channel, 
which runs down by a steep path to the present 
river level. This is an old course of the river. The 
gorge of the Aar used to be regarded as due to 
* GeoL d. SchweiZf vol. i. 
