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 depth of 
intervening sea in all speculations as to geographical 
distribution and the origin of special faunze becomes 
most apparent. 
