352 B.WILLIS — LEWIS AND LIVINGSTON RANGES, MONTANA 



attain a maximum size of 2 centimeters by 5 centimeters, and commonly 

 give rectangular cross-sections. They are set in a dull green ground- 

 mass, with here and there inconspicuous darker spots, where segirine 

 appears in small phenocrysts. Seen by transmitted light, they are a 

 bright emerald green. Under the microscope the.groundmass resolves 

 itself into a matted aggregate of segirine needles and sanidine, with 

 small amounts of nephelite. The tjnguaite was found near the mouth 

 of Coal creek, but no indications of the rock were met at a distance from 

 the North fork of Flathead river. 



