20 THE OPEN BOOK OF NATURE 
Note that all the rocks of the earth at that period 
were purely igneous. 
A time arrived when there were internal disturb- 
ances. Perhaps the earth contracted, as it might 
naturally do with the loss of some of its heat. 
Notice how an apple contracts and wrinkles when it 
gets old and stale ; its surface becomes covered with 
wrinkles and ridges. As the earth cooled and con- 
tracted it also became wrinkled, and ridges were 
formed. In that way land was raised out of the 
sea, and the first continent was formed ; perhaps it 
had a chainof mountains. The igneous rocks were 
thus raised in some part out of the sea ; rain fell upon 
the new land surface, rivers and lakes were formed ; 
changes of temperature giving rise to expansion 
and contraction of the various minerals of which 
they were composed, caused rocks to break up, wind 
scattered dust, and the streams carried boulders, 
sand, and finer particles of stuff into the lakes and 
the sea. In the course of ages the mountains were 
greatly reduced, but in the sea there was a vast 
accumulation of deposited material. This material 
solidified into rocks, say sandstones; then further 
earth movements raised the water-formed rocks out 
of the sea, and they became a new land surface. 
This is some of the work that Nature has been 
doing for millions of years. Rocks that are formed 
in the way I have spoken of are known as “ sedi- 
mentary ” rocks. 
When land was raised out of the sea, it suffered 
the ravages of the sea itself as well as the wear and. 
tear caused by running water, wind, and changes of 
temperature. You will be able to realize what the 
