494 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



The mode (Eosiwal method) is approximately:— 



Quartz 18-2 



Orthoclase 17-5 



Andesine 41-7 



Biotite 11-5 



Hornblende 9-5 



Magnetite -9 



Titanite -3 



Apatite 4 



1000 



In the Norm classification the rock enters the dosodic subrang lassenose, 

 of the domalkalic rang, toscanase, in the persalane order, britannare. For con- 

 venience the analysis of the specimen representing the principal phase of the 

 Similkameen batholith is entered in Col. 2 of Table XXXII. It will be noted 

 that, although these two analyses are exceedingly alike and differ by not so 

 much as would two random specimens from either of the two bodies, yet, 

 according to the system of the Norm classification, the batholith rock must be 

 classified as yellowstonose in the alkalicalcic rang, coloradase, and. thus in a 

 quite different pigeon-hole from that assigned to the dominant phase of the 

 Castle Peak stock. One may seriously question the value of a classification 

 which obscures the fact that the two bodies are chemically almost identical. 

 The writer believes this fact to be of primary importance in the discussion 

 of their geological relations. 



In the older classification this principal phase of the stock is a typical 

 granodiorite. 



Basic Contact Phase. — The stock has a distinctly basified contact-shell, 

 from 200 to 500 yards wide along the existing outcrops. In this shell, quartz 

 is not visible or at least conspicuous, to the naked eye; orthoclase is only a 

 rather rare accessory. The plagioclase averages the basic andesine, Ab 4 An 3 . 

 Hornblende and biotite are present in higher proportion than in the principal 

 phase. In grain and structure the two phases are similar. The specific gravity 

 of the basic phase was found to be 2-811. This value agrees very closely with 

 the specific gravity of the contact phase of the Similkameen batholith, (2-819), 

 showing another indication of the direct genetic connection between the two 

 bodies. This basic phase of the stock has not been- analyzed, but it is clearly a 

 hornblende-biotite diorite rich in accessory quartz. 



Structural Relations. —The area and ground plan of the stock are shown 

 in Figure 35. 



The country rocks are the Cretaceous argillites and sandstones, so folded 

 and faulted as to present dips varying from 40° to 90°. Lines of strike and 

 characteristic dips are illustrated in the diagrammatic map. 



It .can be seen from the map that the stock is not in laccolithic relations ; 

 but only in the field, as one follows the wonderfully exposed contact line, does 

 one appreciate the fullness of the evidence that the plutonic mass is a cross- 





