20 
AMERICA THE OLD WORLD. 
For a table containing the geological periods 
in their succession, I would refer to any modern 
text-book of Geology, or to an article in the u At- 
lantic Monthly ” for March, 1862, upon u Meth- 
ods of Study in Natural History,” where they 
are given in connection with the order of intro- 
duction of animals upon earth. 
Were these sets of rocks found always in the 
regular sequence in which I have enumerated 
them, their relative age would be easily deter- 
mined, for their superposition would tell the 
whole story : the lowest would, of course, be the 
oldest, and we might follow without difficulty 
the ascending series, till we reached the youngest 
and uppermost deposits. But their succession 
has been broken up by frequent and violent al- 
terations in the configuration of the globe. Land 
and water have changed their level, — islands 
have been transformed to continents, — sea-bot- 
toms have become dry land, and dry land has 
sunk to form sea-bottom, — Alps and Himalayas, 
Pyrenees and Apennines, Allegh anies and Rocky 
Mountains, have had their stormy birthdays since 
many of these beds have been piled one above 
another, and there are but few spots on the earth’s 
surface where any number of them may be found 
m their original order and natural position. 
When we remember that Europe, which lies 
before us on the map as a continent, was once 
