RISING AND SINKING OF LAND. 23 
posed of different earthy constituents and enclosed different 
petrifactions. 
The striking differences which so frequently occur be- 
tween the petrifactions of two strata, lying one above 
another, are to be explained in a simple and easy manner by 
the supposition that the same part of the earth’s surface has 
been exposed to repeated depressions and elevations. Such 
alternating elevations and depressions take place even now 
extensively, and are ascribed to the heaving of the fiery 
fluid nucleus against the rigid crust. Thus, for example, 
the coast of Sweden and a portion of the west coast of 
South America are constantly though slowly rising, while 
the coast of Holland and a portion of the east coast of 
South America are gradually sinking. The rising as well as 
the sinking takes place very slowly, and in the course of a 
century sometimes only amounts to some few lines, some- 
times to a few inches, or at most a few feet. But if this 
action continues uninterruptedly throughout hundreds of 
t.ousands of years it is capable of forming the highest 
mountains. 
It is evident that elevations and depressions, such as 
now can be measured in these places, have uninterruptedly 
alternated one with another in different places during the 
whole course of the organic history of the earth. This 
may be inferred with certainty from the geographical distri- 
bution of organisms. (Compare vol.i. p. 350.) But to form a 
judgment of our paleontological records of creation it is ex- 
tremely important to show that permanent strata can only 
be deposited during a slow sinking of the ground under 
water, but not during its continued rising. When the 
ground slowly sinks more and more below the level of the 
