260 GENERALIZATIONS. 



the chains of hills are merely the remains of the former surface 

 of the Miocene ; and in a similar manner the smaller lake-basins 

 of that district may have originated *. 



In the north of Switzerland the waters met the hard and 

 lofty masses of the Jura, and flowed on at their feet until they 

 arrived at places where transverse valleys had cut through 

 chain of the Jura; through these openings the streams rolled 

 from the country. That this grand furrowing was, for the most 

 part, effected at the Drift epoch is shown by the fact that the 

 distribution of the glaciers and of their moraines and boulders is 

 governed by the present formation of the valleys, so that these 

 must have been at that time in existence, as has been already 

 shown (p. 184). The Rhine, also, then flowed in its present 

 bed (pp. 217, 218) ; whilst during the Miocene period the waters 

 took a different direction (vol. i. pp. 303, 304), and the outflow 

 through Alsace was closed. Consequently the erosions of the 

 Miocene coincide in time with the upheaval of the Alps, which 

 took place gradually ; and the rivers must have by degrees ac- 

 quired a greater fall, and their erosive power must have increased. 

 A new system of water-movement then prevailed, deriving its 

 impulse and character from the upheaval of the Alps and the 

 waters flowing down from them. The valleys produced by the 

 upheaval of the mountain district were continued into the re- 

 gion of the Miocene ; and even the river-valleys and lake-basins 



* Professor Desor regards erosion as- the cause of the formation of all lakes 

 of the Miocene district, not merely the small ones (such as the lakes of Greifen 

 and of Pfaffikon), but also the Lakes of Zurich, Constance, and Geneva. He 

 therefore calls them u erosion-lakes." Such erosion, however, could take 

 place only when the water had a fall ; and it must therefore be assumed in the 

 case of these lakes that the bed of their outflow was formerly much deeper, 

 and has been filled up. But this is by no means the case to such a degree as 

 the depth of these lakes would require. Thus the lake of Zurich is in one 

 place 266 metres (or 291 yards) in depth, and its bottom is therefore only 

 142 metres (or 155 yards) above the sea-level, and 123 metres (or 134-5 

 yards) below the level of the Rhine at Basle. Between Zurich and Basle the 

 river passes in many places over rocks in position, as at the Betznau, 323 

 metres (or 353-2 yards) above the sea-level ; and therefore the bed cannot 

 then have been deeper. This renders it improbable that the Lake of Zurich 

 originated only by erosion, and leads rather to the assumption of a local 

 sinking. This applies also to the lakes of Constance and Geneva. (See 

 Studer, " De TOrigine des Lacs Suisses," Bibl. Univ. 1864.) 



