1I 



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 



Rock and location. 



Silica. 



Kbyolite (granitic), top of Terry Teak 



Kliyolite (gnniitic), top of Terry Peak 



Rhyolite, southeast of Teixy Peak 



Saiiidin-tracbyte, ridge east of Terry Peak 



Kliyolite, soutlieast of Terry Peak 



Sanidin-trachyte, hill southeast of Terry Peak 



Sauidiu-trachy te, southeast of Terry Peak 



Rhyolite, uear Deer Mountains 



Rhyolite, southeast of Terry Peak 



Rhyolite, top of Custer Peak 



Rhj-olite, top of Custer Peak 



Phonolite, Black Butte 



Sanidin-trachyte, Black Butte 



Rhyolite, Crow Peak .. 



Sauidin-oligoclase-trachyte, Bear Butte Creek 



Rhyolite, North Peak, Inyau Kara 



Sanidin-trachyte, Center Peak, Inyan Kara 



Sanidin-trachyte, hill west of Inyan Kara., 



Sauidiu-trachy te. Bear Lodge 



Sanidin-trachyte (phonolitic). Little Missouri Buttes. 



Sanidin-trachyte, north of Warren Peaks 



Rhyolite (quartzitic). Gold Ledge, Warren Peaks 



Sanidin-trachyte, White wood Creek 



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 



SoLin 

 acid. 



4.56 



3.12 



2.92 



16.68 



3.74 



8.58 



13.48 



G.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 ammonic molybdate, which, after solution in ammonia, gives a crys- 

 talline precipitate with magnesia mixture, proving the microscopic determi- 

 nation of apatite. 



