526 



GEOLOGY OF THE BLACK HILLS. 



Silica determinations and amount soluble in hydrochloric acid. 



No. 



101 

 103 

 109 

 113 

 120 

 123 

 124 

 127 

 131 

 134 

 135 

 139 

 140 

 141 

 144 

 147 

 149 

 157 

 161 

 167 

 174 

 187 

 213 



Bock and location. 



Rhyolite (granitic), top of Terry Peak 



Ehyolite (granitic), top of Terry Peak 



Rhyolite, southeast of Terry Peak 



Sanidin-trachyte, ridge east of Terry Peak 



Ehyolite, southeast of Terry Peak 



Sanidin-trachyte, hill southeast of Terry Peak 



Sanidin-trachyte, southeast of Terry Peak 



Ehyolite, near Deer Mountains 



Ehyolite, southeast of Terry Peak 



Ehyolite, top of Custer Peak 



Ehyolite, top of Custer Peak 



Phonolite, Black Butte 



Sanidin-trachyte, Black Butte 



Ehyolite, Crow Peak 



Sanidin-oligoclase-trachyte, Bear Butte Creek 



Ehyolite, North Peak, Inyan Kara 



Sanidin-trachyte, Center Peak, Inyan Kara 



Sanidin-trachyte, hill west of Inyan Kara 



Sanidin-trachyte, Bear Lodge 



Sanidin-trachyte (phonolitic), Little Missouri Buttes 



Sanidin-trachyte, north of Warren Peaks 



Ehyolite (quartzitic), Gold Ledge, Warren Peaks 



Sanidin-trachyte, Whitewood Creek 



Silica. 



72. 35 

 71.13 



75.09 

 58.83 

 72.27 

 63.56 

 57.75 

 73.22 

 72.22 

 68. 62 

 72.33 

 56.32 

 58.53 

 67.36 

 65.46 

 73.18 

 60.51 

 61.88 

 60.77 

 59.06 

 52.02 

 79.89 

 61.98 



Sol. in 

 acid. 



4.56 



3.12 



2.92 



16.88 



3.74 



8.58 



13.48 



6.67 



5.31 



5.62 



5.61 



24.08 



18.59 



3.54 



10.09 



4.21 



6.32 



6.55 



15.33 



29.25 



23.14 



6.45 



9.93 



[139] gelatinizes strongly in hydrochloric acid and does not give any 

 phosphoric acid reaction with amnionic molybdate. 



[174] does not gelatinize, and gives an abundant yellow precipitate 

 with amnionic molybdate, which, after solution in ammonia, gives a crys- 

 talline precipitate with magnesia mixture, proving the microscopic determi- 

 nation of apatite. 



