THE STUDY OF THE ROCKS 



rock is firmly fixed to the glass we proceed as before, 

 but in this case the final grinding and polishing 

 must be very carefully carried out. Towards the 

 end of the operation our original lump of rock will 

 be reduced to the thinness of a cover slip and to its 

 fragility. Having given the finishing touches with 

 jeweller's rouge, we put the glass, with its attached 

 rock section into a bottle of xylol (to be obtained 

 from any chemist). The xylol dissolves the Canada 

 Balsam and the rock section falls from its support. 

 A further washing in clean xylol should be given 

 and then the section is ready for mounting, which 

 is best done in Canada Balsam. The section may 

 be carefully fixed to the slide with a drop of Balsam 

 or it may be covered with a cover slip, in the usual 

 manner. 



In our concluding chapter we give hints on slide 

 making and addresses of firms who supply slides. 

 Our advice in that chapter is to prepare one's own 

 slides where possible; in the case of rock sections, 

 however, we must change our advice, only the 

 microscopist of unlimited leisure can find time to 

 make his own slides. 



One of the most interesting branches of rock study 

 deals with the fossil remains of plants and animals. 

 Fossils are interesting in themselves : they are doubly 

 interesting because they tell us more than we could 

 ever have discovered without them, concerning the 

 living forms which inhabited the earth at different 

 periods. Geologists know the order in which the 

 various secondary rocks were formed and by study- 



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