Jo urn. Q. M. C. 



Ser. 2, Vol. XII., PI. 35. 



* O- Q> 



~i 





S short edgr 



Thickness \ , . 

 of section) m cr<m 



-etord'Jtion] 340 miermiiUmetra 



B/refringence /2/nilleums or '01Z 



rfc refractive indices of crystal of Me same mt/terff! or /Ac 

 ma/yin of the rock -shce rasied between 1 644 and / 65$ 



Scale 



ttfff 



tf Microns 

 loo 230 



-rhtcKncss rrr f r 



300 



JL 



Magnification 63 times 



Determination of Minerals. 



(By permission of the Geologists' Association.) 



