406 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



Analysis of principal phase, Rock Creek chonolith. — Continued. 



Mol. 



HoO at 110°C .27 . . 



H 2 above 110°C 315 -175 



P 2 s .55 -004 



C0 2 43 -010 



99-70 



Sp.gr 2-621 



In many essential respects this rock is mineralogically and chemically like 

 the classic types described by Brogger, Rosenbusch, and Backstrom.* For conven- 

 ience the average analysis of seven of those types is given in Col. 4, Table XXVI. 

 Column 5 shows the range of variation in the oxide proportions. The chemical 

 difference between the Norwegian and British Columbia rocks are largely 

 explained by the higher proportion of femic minerals in the latter. The large 

 amount of water liberated above 110° C. is almost certain to have come princi- 

 pally from the glassy base. Since the rock is so fresh it does not seem possible 

 tbat this water was introduced during weathering; it must, seemingly, be 

 regarded as of primary origin, though it has been responsible for, or, at least 

 co-operated in, the partial zeolitization of the glassy base. The British Col- 

 umbia rock rock is further notable for relatively high percentage of BaO and 

 SrO, two oxides which were not determined in the Norwegian specimens. 



Table XXVI. — Analyses of rhomb-porphyries and related rocks. 





1 



2 



3 



4 



5 



6 



SiO„ 



TiO„ 



52 43 

 ■86 



19 18 

 351 

 208 



2 61 

 371 



•42 



■35 



485 



595 



■27 



3 19 

 ■42 

 tr. 



99 83 



5183 



•86 



18 25 



426 



146 



328 



408 



•42 



■43 



4-08 



5-75 



•27 



3 15 



55 



•43 



52 



18 

 3 

 1 



2 

 3 



4 

 5 



3 



13 



86 

 72 

 90 

 77 

 95 

 90 

 42 

 39 

 77 

 85 

 27 

 17 

 49 

 22 



57 19 



54 0— 60 72 



51 02 



•56 



Al 2 O s 



Ke„O s 



FeO 



19 44 



| 6 44 



1'28 

 3 10 



16-48— 22 15 



2-08—1079 



•70— 193 

 242- 401 



16-82 

 3 58 

 366 



MgO 



CaO 



SrO 



BaO 



3'38 

 606 

 •30 

 •49- 



Na„0 



632 

 444 



} 134 



304— 839 

 324— 630 



•60— 3 25 



349 



K.iO 



H 2 0-.... 



H^O+ 



744 

 275 



P„0 5 



•49 



CO„ 





















99-70 



99-81 



99 55 



100 04 



1. Chilled phase, Rock creek chonolith. 



2. Central phase, Rock creek chonolith. 



3. Average of 1 and 2. 



4. Average of seven types of Norwegian rhomb-porphyry. 



5. Range of oxides in seven types averaged in 4. 



6. Average of four types of basic syenite (borolanose) from the Highwood mountains; L. V. 

 Pirsson, Bull. U. S. Geol. Surv., No. 237, 1905, pp. 172-3. 



* Analyses taken from Osann's Beitraege zur Chemischen Petrographie, 1905, pp. 

 31 and 138, and from Rosenbusch's Elemente der Gesteinslehre, 1901, p. 286. 



