2o 4 PREHISTORIC EUROPE. 



the phenomena in question. Let me briefly state the grounds 

 for believing that the under strata of the mer de glace flowed 

 round the south coast of Norway. At various points upon that 

 coast, as near Dybvaag, at Bliksund between Lillesand and 

 Christiansand, and even as far north as the district of Jsederen, 

 occur several erratics of zircon-syenite, and other rocks which 

 could only have been derived from Skien, Laurvig, and Fred- 

 riksvsern in Langesundfjord near the opening into Christiania- 

 fjord. 1 These are the rocks which have already been referred 

 to as having been obtained by Mr. Helland in the boulder- 

 clay of Holderness. Now the Admiralty's charts show that a 

 deep hollow extends all round the south coast of Norway — 

 the limits of which are indicated upon my map by the two 

 dotted lines. In Bonus Bay, we find depths ranging from 700 

 up to nearly 2000 feet. Opposite Arendal the depth is even as 

 much as 2580 feet. The trough seems to become shallower off 

 the coast of Jsederen, where, however, it is still more than 1000 

 feet deep. In the Skaggerak, just outside of the trough, the sea 

 does not average more than 150 feet in depth, so that in Bonus 

 Bay the hollow is some 2400 feet deeper. Even as far west 

 as Jsederen the bed of the great hollow is still 700 or 800 

 feet below the average level of the sea-bottom immediately 

 to the south and south-west. Now it is evident that the lower 

 strata of the great mer de glace could not ignore this profound 

 hollow, but would naturally tend to follow it in its course 

 to west and north-west ; and thus boulders and morainic 

 material derived from the Christiania district would tend to 

 travel in a direction at right angles to that followed by the 

 upper strata of the ice which flowed (as the striae in the 

 fiords and on the high grounds of Southern Norway attest) 

 towards the south. Notwithstanding that westerly determina- 

 tion of the under strata, however, the influence of the upper 

 strata could not but be propagated to a great depth in the mer 

 de glace, and thus the ice below would gradually tend to be 



1 Kjerulf : Udsigt over dct sydlige Norges Geologi, p. 31. 



