chap, x.] CONTINUITY OF THE CHALK. 473 



newer secondary beds, although some of them, such as 

 the Alps and the Pyrenees, have received great acces- 

 sions to their height in later times. All these newer 

 beds have therefore been deposited with a certain re- 

 lation in position to certain main features of contour 

 which are maintained to the present day. Many oscil- 

 lations have doubtless taken place since, and every 

 spot on the European plateau may have probably 

 alternated many times between sea and land; but it is 

 difficult to show that these oscillations have occurred 

 in the north of Europe to a greater extent than from 

 4,000 to 5,000 feet, the extreme vertical distance be- 

 tween the base of the tertiaries and the highest point 

 at which tertiary or post-tertiary shells are found on 

 the slopes and ridges of mountains. A subsidence of 

 even 1,000 feet would, however, be sufficient to pro- 

 duce over most of the northern land a sea 100 fathoms 

 deep, deeper than the German Ocean ; and an eleva- 

 tion to a like amount would connect the Shetland and 

 Orkney Islands and Great Britain and Ireland with 

 Denmark and Holland, leaving only a long deep Fjord 

 separating a British peninsula from Scandinavia. 

 When we bear in mind the abundant evidence 

 which we have that these minor oscillations, with a 

 maximum range of 4,000 to 5,000 feet, have occurred 

 again and again all over the world within compara- 

 tively recent periods, alternately uniting lands and 

 separating them by shallow seas, the position of the 

 deep water remaining throughout the same, the im- 

 portance of an accurate determination of the dejDth of 

 intervening sea in all speculations as to geographical 

 distribution and the origin of special faunae becomes 

 most apparent. 



