THE STUDY OF THE ROCKS 



its very beginnings if we are really to understand 

 what we see beneath the microscope. 



In the hand, a lump of rock, say of granite, may 

 be of exceeding beauty. The body of the rock is, 

 perhaps, a delicate pink, scattered here and there 

 are the flat glittering plates of mica and brilliant 

 crystals of quartz. Other rocks, less common, vie 

 with the rare gems for beauty of colouring and 

 lustre. As thin microscope sections these once 

 gorgeous specimens are colourless, dull and, unless 

 we understand them, uninteresting . 



There are, however, many mineral substances 

 which we may study with advantage for, if our 

 investigations do not take us very far towards 

 elucidating the story of the rocks, we shall at any 

 rate discover something that is new to us. We may 

 well commence our studies with the examination 

 of ordinary sand. This is not a rock, you will 

 probably exclaim. You are right but one day it 

 may be a rock, it all depends upon circumstances. 



Before we take out our microscope let us have 

 a short talk about rocks in general, then we may 

 understand better where we are. Rocks of one 

 kind and another make up the crust of the earth, 

 that is pretty obvious anyway. Thousands and 

 thousands of years ago, how many we are not pre- 

 pared to guess, this old earth of ours was a sphere 

 of molten rock. Needless to say it was far too hot 

 for any plants or animals to dwell upon it. Very, 

 very gradually the outer crust cooled down and in 

 time it became sufficiently cool to support animal 



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