312 M. Ami Bouc on the Palceohydrography 



The comparison of the Jura in the Alps and Mediterranean 

 countries with that in Central Europe, has often induced 

 geologists to acknowledge in that time two seas of very 

 different depth as well as very divided seas. Lastly, the 

 peculiarities of the Muschelkalk in the German Alps, in Supe- 

 rior Italy, and in Superior Silesia, give proofs of the existence 

 then of a sea channel where now the Alps partly raise their 

 heads. (Zeitsch. d. Deutsch Geol. Gesch., Berlin, 1849, vi. 

 p. 246). 



In taking another view of the subject, one finds still an- 

 other mode of coming to conclusions. I mean, to make use 

 of all that we know of the various thickness of the forma- 

 tions, and the variation in the same formation, as well as 

 of the absolute height they attain in different countries. 

 But on this our information is still very small. 



I must remark, 1st, That the fresh- water formations, like 

 the alluvial and Travertine deposits, are to be found at very 

 different heights and in very different thickness ; 2d, That 

 the various heights of actual seas shew the former existence 

 of a sea in the same way at different altitudes. Besides, we 

 have proofs that seas were formerly much more numerous, 

 and sometimes placed on levels one above the other. This 

 gives an idea how a part of the water has found room in 

 older times on the earth. The salt-water sea has been con- 

 verted into fresh- water before it became empty, or after 

 having become partly empty. If we had, for instance, the 

 medium value of the depth of sea in the old alluvial period, 

 we could say how deep that sea was in Northern Europe 

 when the erratic phenomena took place, because the boulders 

 indicated its height in the southern part of this basin, where 

 they came upon the ice floating, and not by glaciers, as in 

 Scandinavia. 



On the other hand, one could fall into error if one would, 

 from the results gained in this way, conclude about the depth 

 and absolute height of the sea at the foot of the Alps during 

 these times, or during the tertiary period, because probably 

 a sea was there on a higher level than that of Northern 

 Europe. 



'3d, The difference in the thickness and absolute height of 



