1855.] SHARPE— ELEVATION OF THE ALPS. 109 



out of the waters : at the earliest of these periods the Alps formed 

 merely a cluster of small islands, with nearly precipitous sides 

 dipping. at once into very deep water, and surrounded by an open 

 ocean, the highest being 6750 feet above the sea. At the second 

 period there were a few large islands, rising to above 7000 and 8000 

 feet, separated by narrow channels, with deeply indented shores, 

 surrounded by a deep sea, and forming a group somewhat resembling 

 the Hebrides. At the third period the group would have more 

 resembled the north of Scotland, forming a long narrow island, in- 

 dented with deep friths, but with its highest peaks 10,000 and 

 11,000 feet above the sea, and therefore probably capped with 

 snow. 



It is probable that a closer examination would find other lines of 

 erosion, intermediate between the three here noted ; but, if they 

 exist, they are far less marked, and consequently less important than 

 the three lines here described. They may also perhaps be found 

 below my lowest line ; but it will require great care in tracing them ; 

 for, as we descend below that level, the vegetation interferes more 

 and more with our observations, and cultivation often modifies the 

 ground ; besides which, the lower heights lie principally among 

 stratified rocks, whose forms are as much due to the horizon tality or 

 inclination of their strata as to subsequent erosion. 



As the two lower lines of erosion have been traced equally across 

 the eocene and all the older formations, I think it is evident that 

 these erosions took place at a late period, — probably after all the 

 strata of Switzerland (except the drift) lay in their present positions 

 relatively to one another : and there are no circumstances connected 

 with the uppermost line to lead us to place it before the same period : 

 the change indicated by these observations is the elevation of the 

 ^* whole country out of the sea, as has been going on for several 

 centuries in Sweden and Norway. 



This elevation seems to have been very uniform over the whole of 

 Switzerland ; or, if it has been greater at one end of the country than 

 the other, the difference must be very trifling ; my observations give 

 a uniform level to the lines of erosion for about ninety miles from 

 N. to S., and a very near approach to uniformity from E. to W. 

 for nearly 200 miles. And, as stated at starting, I think that the 

 error in their general results cannot amount to 200 feet. 



The amount of degradation which the Alps have undergone during 

 the periods here referred to seems to correspond with the enormous 

 accumulation of rolled detritus collected on their flanks. The area 

 of the great valley of Switzerland between the Alps and the Jura is 

 not very different in extent from the area of that portion of the Alps 

 of which the detritus would be carried northwards. 1 do not know 

 whether any one has made an estimate of the average thickness of 

 the deposit of rolled detritus throughout that valley, which I should 

 estimate at several hundred feet. This therefore shows the abstrac- 

 tion of the same thickness of matter from the whole of the Alps, or 

 of a much greater thickness from the more limited area exposed to 

 the reach of the waves during their elevation. 



VOL. XTI. — PART I. I 



