Cn. XVI.] 



IC KBERGS. 



870 



I 





V 





el 







ing 



At 



w 



■ i 



" 



"" 



been deepened artificially several feet, with a view of prevent- 

 ing the Marj elen See from rising to its full height, thereby 

 lessening the magnitude of the floods caused by the bursting 

 of the icy dam. The Mayor or Castellan of Viesch showed 

 me an old document, from which I learnt that towards the 

 end of the 17th century (1683) the government of the Can- 



tor draining" 



the 



ton of Valais were busy with a scheme 

 Marj elen See, and diminishing the volume of its periodical 

 inundations. This record is valuable, as teaching us that both 

 the ordinary and exceptional condition of the lake, about two 

 centuries ago, were the same as now. 



Those geologists who have contended that the old beaches 

 or parallel reads of Lochaber in Scotland were formed on the 

 margins of sheets of water blocked up by ice, have sometimes 

 been met with the objection that we can hardly imagine such 

 a blockage to be permanent, or to retain the water steadily at 



the same level. Now 



admitted that each, c 



the constancy of the level, it is 

 Scotch shelves coincides with a 



watershed or col dividing the glen in which the shelf occurs, 

 from an adjoining glen. Provided the dam of ice be higher 

 than this watershed, it may evidently vary in magnitude to 

 any amount without in any way affecting the level of the 

 beach or marginal terrace of detrital matter. But we also 

 learn from the Marj elen See, that even if the ice-dam perio- 

 dically gives way, and is renewed after months or years, 

 it will not, if the physical geography of the district remains 

 unaltered, affect the constancy of the level at which the prin- 

 cipal beach or road is formed.* 



Icebergs. — In countries situate in high northern latitudes, 

 like Spitzbergen, between 70° and 80° N., glaciers, loaded with 

 mud and rock, descend to the sea, and t 



them float off and become icebergs. 



Scoresby counted 500 

 s 69° and 70° K. which 



from 



measured from a few yards to a mile in circumference. f Many 

 of them were loaded with beds of earth and rock of such 



In the < Antiquity of Man ' I have eluding with the papers of Mr. Jamieson, 





given a description of the ' parallel 

 roads ' alluded to, and have referred to 

 the numerous authors on the subject, con- 



of Ellon, in support of the glacier-lake 

 theory. 



t Voyage in 1822, p. 233. 



