22 THE OPEN BOOK OF NATURE 
out of the sea, and even to bring a new continent 
into being. 
Many young people seem to be under the impres- 
sion that great upheavals and tremendous earth- 
quakes are principally responsible for changes in 
the earth’s surface. Asa matter of fact, water has 
done far more than they ; it has reduced mountains, 
hollowed out ravines, laid down fertile plains, made 
sheltered valleys, and deposited the rocks of great 
continents. The earth movements which have 
raised land out of the sea have been of a very 
gradual kind, occupying ages. Nature does her 
grandest work little by little. 
In addition to the rocks which have been formed 
by fire and deposited by water, there are other 
rocks formed by chemical agency, others known as 
‘ organically-formed ” rocks, and still others which 
are called ‘‘ metamorphic.” Perhaps I shall help 
you if I enumerate and describe the various rocks 
as follows : 
1. Ienzous Rocks : 
(a) Plutonic. 
(b) Volcanic. 
2. STRATIFIED Rocks : 
(a) Sedimentary Deposits. 
(6) Chemically-formed. 
(c) Organically-formed. 
3. MmTAMORPHIC ROOKS. 
The Ianzous Rocks have been formed from the 
molten material of the earth’s original substance ; 
they are generally crystalline, and exist in large 
unstratified masses. They bear no fossils. They 
occur either as plutonic rocks, or volcanic. 
