BLACK HILLS GEOLOGY. 273 



Chemical Composition of the Phonolites. 



In their chemical composition the phonolites vary only within 

 narrow limits. 



On page 272 will be found a series of analyses. 



Phonolites. 



/. Phonolite from the summit of Ragged Top Mountain. 

 Contains nepheline, orthoclase, aegirine, magnetite and melanite 

 garnet. This rock is a typical phonolite. Analysis by Pro- 

 fessor F. C. Smith, Deadwood, South Dakota. 



Tinguaites. 



//. Tinguaite from dike on Ulster claim of A. J. Smith, near 

 Preston, South Dakota. Analysis by Professor Flintermann, 

 Deadwood, South Dakota. 



///. Tinguaite. — Dike in Squaw Creek, below Gushurst mine. 

 Typical tinguaitic texture. Analysis by Professor Flintermann, 

 Deadwood, South Dakota. 



Trachytoid Phonolites. 



With Tinguaitic Aspect. 



IV. From the sheet at the junction of Annie and Rose Spring 

 ■creeks. Analysis by Professor Flintermann, Deadwood, South 

 Dakota. 



V. Rather fine-grained variety from sheet in Annie Creek, 

 near loop of Burlington and Missouri River Railroad. Analysis 

 by Professor Flintermann, Deadwood, South Dakota. 



VI. Trachytoid phonolite from Annie Creek near Loop on 

 the Burlington and Missouri River Railroad. Analysis by Pro- 

 fessor Flintermann, of Deadwood, South Dakota. 



VII. From same locality as No. VII. Professor Flintermann, 

 analyst. 



VIJI. Sheet near last. Analysis by Professor Flintermann, 



