THE CENTRAL PLAIN. 
47 
only contain thick deposits of river gravel, etc., but 
also show the usual terraces along their sides. 
The remarkable case of the Venoge has been 
already described (vol. i. p. 227). 
The Aar at Aarberg and Schinznach, the Reuss 
at Mulligen, and the L.immat at Baden, have sawn 
their way through Jurassic ridges. The Sarine cuts 
through several mountain ranges.* If these had 
risen more rapidly than the rivers could cut through 
them, lakes must have been formed, and it is even 
possible that for a time such lakes may have 
existed. 
It is clear then that the courses of the ancient 
rivers were in many cases very different from those 
of the present day. 
But although these considerations explain to a 
great extent the general direction of the river courses, 
there are not a few cases, as for instance in the 
north of the Canton of Vaud, and south of Fribourg, 
where they are far from easy to understand. Gillieron 
points out that the character of the Flysch which 
forms the district makes it difficult to distinguish the 
structure of the mountains, and that it is impossible 
at present to form any idea as to the original relief. 
* Musy, “Disc. pron. ii I’ouv. de la 74^ sess.,” Ann. Soc. 
Ilelv. Fribourg, iSqi. 
