Rock from the Highwood Mountains of Montana. 323 



the ordinary plagioclase basalts or granite to rhyolite. It is 

 closelj related to theralite, shonkinite, and ijolite, but cannot 

 be classed under any of these types and must therefore be dis- 



Micro-drawiDg of Missourite x 6 ; P = pyroxene, = olivine, & = biotite 

 L = leucite. 



tinguished by a special name of its own. We have therefore 

 called it missourite from the Missouri Eiver, the most promi- 

 nent and best known geographical object in the region where it 

 occurs. 



"Washington and New Haven, May, 1896. 



