KOSCOPICAL INVEST! 137 



lent l>) this means is enabled to examine the 



<lti.il minerals of a rock, and may obtain the most 



sitely |K-rtc<t crystals whose optical characters, 



crystal lotfra | >hic forms, inclusions, and intergrowths, he 



may study as easily ai if he had large specimen* to 



hand 



Thin Sttti0*s.'\'o prepare slices of rocks and 

 mnu-rals for the mirrosmj < it is not necessary to 

 procure a costly and unwieldy set of apparatus, nor 

 to go through a lengthened course of training. The 

 operation is facilitated, indeed, by the possession of 

 a machine f< thin slices, and for reducing 



and when mounted on glass. A 



veil adapted for both purposes was devised 

 years ago by ' Jordan, and may be had of 



Messrs. Cotton and Johnson, Gerrard Street, Soho, 

 n, for jio:ios. Another slicing and polishing 

 machine by Mr. F. G. Cuttell, 47 Rath- 



bone Place, W., London, costs 6 : IDS. But these 

 machines are rather unwieldy to be carried about the 

 country by a field-geologist Fuess of Berlin supplies 

 two small and convenient hand - instruments, one for 

 slicing, the other for grinding and polishing. The slicing 

 machine is not quite so satisfactory for hard rocks as 

 one of the larger more solid forms of apparatus worked 

 by a treadle. But the grinding machine is exceedingly 

 useful, and might be added to a geologist's outfit without 

 material inconvenience. If a lapidary is within reach, 

 much of the more irksome part of the work may be 

 saved by getting him to cut off thin slices. The thick- 

 nest of each slice must depend greatly upon the nature 



