196 Weed and Pirsson — Bear paw Mountains of Montana. 



marked, that there oannot be a possibility of doubt upon this 

 point. It consists of large, white, well-formed pseudo-leu- 

 cites and smaller, white or pinkish sodalites and noseans 

 thickly crowded in a dense, dark green groundmass. An 

 occasional augite or feldspar phenocryst is also seen. The 

 microscope shows the pseudo-leucites so be made up of alkali- 

 feldspar and nephelite. The groundmass is composed of 

 alkali-feldspar, nephelite, and gegirite needles. For further 

 details the reader is referred to the former paper. A more 

 detailed study of the feldspars shows them probably to be 

 soda orthoclases or anorthoclase. They have, moreover, the 

 watered, wavy, moire appearance which has been found to be 

 so characteristic a microstructure in the alkali feldspars of 

 these rocks, and which is in reality a very useful diagnostic 

 character. 



The same rare minerals of unknown character are also pres- 

 ent in the new material. 



A complete analysis of this interesting type, by Dr. H. N. 

 Stokes, is given in No. I. 





I. 



II. 



la. 



SiO,... 



.. 51-93 



52^91 



•8655 



Al 



20-29 



19-49 



4-78 

 2^05 



1970 



FeO ... .. 



3-59 



•0224 



FeO 



1-20 



•0166 



MgO 



•22 



•29 



•0055 



CaO 



1-65 



2^47 



•0294 



Na,0 



8-49 



7^13 



1367 



K,6 



9-81 



7-88 

 M9 



1041 



H,0— 110° .. 



.. •lO) 

 -99 j 





H,0-fllO° ... 





TiO, 



-20 



none 



0020 



co; 



-25 



none 



•48 



0057 



Fl... 



-2V 



0142 



CI 



-70 



•53 



0196 



SO3 



-67 



•52 



0070 



p6 



•06 



trace 

 •44 

 •09 





MnO 



trace 





SrO 



•07 





BaO.... 



•09 









LiO 



_ . trace 



trace 





0=C1, Fl 



100^58 



•27 



100-31 



100-25 

 •12 



100-13 



I. Leucite tinguaite, Beaver Creek, Bearpaw Mountains, Mon- 

 tana. H. N. Stokes anal. 



