THE STUDY OF THE ROCKS 



and vegetable life. Then there were rivers and seas 

 and then came, from time to time, rain and wind 

 and frost and even earthquakes. The earthquakes 

 cracked the crust of the earth, moisture entered 

 the cracks and, when the frosts came, pieces of rock 

 were broken away, owing to the expansion of the 

 moisture in the cracks as it became converted into 

 ice. The rain and wind helped to carry the broken 

 pieces of rock, ever downwards towards the sea, but 

 before the sea was reached the big boulders became 

 broken up, by their buffeting, into shingle and sand 

 and mud. In the course of long ages, longer than 

 it is easy to imagine, these broken pieces of rock, 

 gathered together as we have seen from various 

 districts, may have been left high and dry, for the 

 face of the earth has not always been as we know 

 it now. 



In time all the little particles became welded 

 together to form a new kind of rock. Sometimes 

 animals and plants were buried in the mud destined 

 to become a rock and their parts were so well pre- 

 served that they may not only be recognised by 

 present-day scientists, but in many cases their 

 structure may be made out so well with the aid of 

 a microscope that no one would guess they had been 

 buried thousands of years ago. 



New rocks have been formed not only by the 

 breaking up and welding together of the original 

 earth's crust, but by animal and plant remains. In 

 some places, in past ages, billions and billions of 

 little shell-fish have lived in the waters, died there 



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