EXPLANATION OF PLATE. 



The upper ipectram i> that of the spark between cadminm terminals, and the 

 numbers indicate wave-lengths. 



The seven numbered spectra ire kathodo-luminescence spectra of the fol- 

 lowing : 



l Fluorite from Amelia Court-Houae, Virginia. 



2. Fluorite from Trumbull, Conn. 



3. Fluorite from Westmoreland, N. II. 



4. Fluorite from Hardin Co., Ohio. 



5 Purple fluorite from Weardale, England. 



6. Green fluorite from Weardale, England. 



7. Yellow fluorite from Weardale, England. 



