1855.] SHARPE — ELEVATION OF THE ALPS. 121 



Theoretical Conclusions. — It would be very interesting to fix the 

 period at which the elevation of the Alps out of the waters took 

 place, of which the traces of water-levels here described are 

 the records. To accomplish this we must find the latest formation 

 in which we can observe levels corresponding to those which I 

 have established. As the objects of my visits to the Alps confined 

 me principally to the higher mountains, I could not extend my 

 observations in the Tertiary Lowlands of Switzerland ; and thus 

 I can only say with certainty that the elevation included the Eocene 

 Rocks and the elder Nagelfluh which rest on them. But I have 

 little doubt that the elevation took place at a much later period, 

 after the deposit of all the Tertiary Formations. I arrived at that 

 conclusion by looking at the subject from a different point of view. 

 Every elevation of mountains on a large scale must have left its record 

 in an accumulation of debris round their base. If we look back- 

 wards in the history of the Swiss Alps, we find the earliest accu- 

 mulation of this kind to be the VerrucanOy a coarse conglomerate 

 marking the first elevation of the Swiss Alps through the then crust 

 of the earth. Towards the close of the Jurassic period we again 

 find conglomerates, some calcareous, others sandstones (which have 

 sometimes been confounded with the earlier Verrucano), marking 

 another period of great elevation. At the end of the Eocene period, 

 the older Nagelfluh, the enormous thickness of which is seen at the 

 Rigi and neighbouring mountains, points out the period of that 

 great elevation when, the central masses of the Alps being thrust 

 upwards for the last time through the crust of the earth, the moun- 

 tains received their present form, and the Secondary Rocks on their 

 flanks were thrown into the distorted position which they now 

 occupy. The alternations of the beds of gravel with the marine 

 and fresh water deposits of the Molasse point to a long epoch of 

 alternate elevation, depression, and elevation, which are probably 

 contemporaneous with violent movements below the great central 

 valley of Switzerland, on a line parallel to the axis of the Alps, 

 to which the Molasse and the old Nagelfluh owe their disturbed 

 position and their dip towards the Alps for so great a distance. 



After that period the whole country must have again sunk below 

 the sea, and the elevation to which this present communication 

 refers followed at a still later period, raising the whole region up 

 uniformly en masse out of the ocean without disturbing the relative 

 positions of its parts ; and to this movement we may naturally attri- 

 bute the deposits of gravel and boulders spread irregularly over the 

 Lowlands of Switzerland, and thus place this movement after the 

 conclusion of the Tertiary period. 



I have already pointed out (p. 116) that the moraines which 

 mark the greater extension of glaciers at a former period sometimes 

 rest on terraces of alluvium in the valleys and on the so-called dilu- 

 vium of the plains, showing us that the extension of the glaciers 

 followed the accumulation of those deposits which I suppose to 

 have been formed during the elevation of the Alps out of the ocean. 

 An increase of altitude of the Alps of between 1500 and 2000 feet 



