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GEOLOGICAL MEMOIRS, 



throughout, although there are several intercalated beds of fresh- 

 water origin ; and from this, in connection with other facts, we regard 

 the Molasse to have been deposited in water of a uniform and gene- 

 rally slight depth, in a locality where marine and freshwater condi- 

 tions occasionally replaced each other. 



The Molasse without doubt sulfered a slow and continuous down- 

 ward movement, so as to maintain the moderate depth above indi- 

 cated, notwithstanding the continual filling up by new depositions. 

 Hence we conclude that a fissure existed between the Molasse and the 

 Secondary rocks of the Alps (which have not participated in the sub- 

 sidence), without doubt in consequence of the previous elevation of 

 the latter. 



2. The Aar near Berne, the Sarine near Freiburg, and other rivers, 

 have serpentine courses, like rivers of low plains with little fall, 

 although their deeply-cut channels, traversing an undulating country, 

 have steep banks 30 or 40 metres high. The stair-like terraces of the 

 river-beds show that these erosive operations alternated with periods 

 of rest. The material thus cut through generally consists of " old 

 alluvia," i. e. gravel and sand with indistinct horizontal stratification ; 

 but often in the lower portion of the channel, and to the height of 

 1 metres, the perpendicular banks are composed of Molasse. 



A stream, however, that has force and fall enough to excavate so 

 deep a channel, can no longer describe a serpentine ; hence, these 

 rivers must at first have flowed over ground having only a slight de- 

 clivity, but which, after the serpentine course was formed, became 

 more and more steep, thus giving rise to the deep cuttings above- 

 mentioned. These conditions may have simply happened thus : — 

 the upper part of these river-courses has been gradually raised by the 

 elevation of the continent; and this is proved, — 1. by the traces of a 

 previous filling up of the Alpine valleys some hundred feet above the 

 present surface of the rivers, and, 2. by the preservation of the hori- 

 zontality of the strata, — in contrast with the verticality and folding of 

 the Molasse beds previously caused by secondary Alpine strata. 



The elevation of these alluvia can only have taken place subse- 

 quently to the distribution of the erratic boulders, as the serpentine 

 river-courses cut through gravel and loam, inclosing large Alpine 

 blocks, which, however, are never found on the terraces of the river- 

 beds, except where they have fallen down from the undermining of 

 the banks. 



The succession of the movements above indicated is as follows : — 



1 . Elevation of the Alpine district before the Molasse-period. 



2. Subsidence of the district bordering the Alps during the 



Molasse-period. 



3. Elevation of the Molasse and the upcast of its strata. 



4. Deposition of the old alluvia in the Alpine and Molasse 



valleys. 



5. Deposition of the Erratics. 



6. Continental elevation of the Alpine district. 



[T. R. J.] 



