72 
ELEMENTS OF GEOLOGY. 
on the retiring of the annual floods. Aqueous rocks of 
equal antiquity extend for hundreds of miles over the lake- 
district of North America, and exhibit in like manner a 
stratification nearly undisturbed. The Table Mountain at 
the Cape of Good Hope is another example of highly ele¬ 
vated yet perfectly horizontal strata, no less than 3500 feet 
in thickness, and consisting of sandstone of very ancient date. 
Instead of imagining that such fossiliferous rocks were al¬ 
ways at their present level, and that the sea was once high 
enough to cover them, we suppose them to have constituted 
the ancient bed of the ocean, and to have been afterwards 
uplifted to their present height. This idea, however start¬ 
ling it may at first appear, is quite in accordance, as before 
stated, with the analogy of changes now going on in certain 
regions of the globe. Thus, in parts of Sweden, and the 
shores and islands of the Gulf of Bothnia, proofs have been 
obtained that the land is experiencing, and has experienced 
for centuries, a slow upheaving movement.^ 
It appears from the observations of Mr. Darwin and oth¬ 
ers, that very extensive regions of the continent of South 
America have been undergoing slow and gradual upheaval, 
by which the level plains of Patagonia, covered with recent 
marine shells, and the Pampas of Buenos Ayres, have been 
raised above the level of the sea. On the other hand, the 
gradual sinking of the west coast of Greenland, for the space 
of more than 600 miles from north to south, during the last 
four centuries, has been established by the observations of a 
Danish naturalist. Dr. Pingel. And while these proofs of 
continental elevation and subsidence, by slow and insensible 
movements, have been recently brought to light, the evi¬ 
dence has been daily strengthened of continued changes of 
level effected by violent convulsions in countries where earth¬ 
quakes are frequent. There the rocks are rent from time to 
time, and heaved up or thrown down several feet at once, 
and disturbed in such a manner as to show how entirely the 
original position of strata may be modified in the course of 
centuries. 
Mr. Darwin has also inferred that, in those seas where cir¬ 
cular coral islands and barrier reefs abound, there is a slow 
and continued sinking of the submarine mountains on which 
the masses of coral are based; while there are other areas of 
the South Sea where the land is on the rise, and where coral 
has been upheaved far above the sea-level. 
Alternations of Marine and Fresh-water Strata. —It has been 
shown in the third chapter that there is such a difference be- 
* See ‘‘ Principles of Geology,” 1867, p. 314. 
