STRUCTURAL AND STRATIGRAPHICAL RELATIONS 449 



selected the sample which has been kindly analyzed by Dr. Henry S. 

 Washington with the following results : 



SiO, 63.46 Na,0 5.19 



TiO, 0.12 K„0 3.56 



AUO3 16.83 H.0+ 0.83 



Ci-oOa none H^O 0. 03 



Fe^Os 2.23 F.O, 0.28 



FeO 1.88 SO3 0.05 



MyO 0.17 CO2 none 



MgO 1.13 ZrO, none 



CaO 4.00 CI notdet. 



BaO 0.09 



Total 99.85 



The norm was calculated by Dr. Washington as follows : 



Quartz 10.74 Hypersthene 2.22 



Orthoclase 21.13 Magnetite 3.25 



Albite 44.01 Ilmenite 0.30 



Anorthite 11 . 95 Apatite 0. 67 



Diopside 4.86 



The symbol of the norm in the quantitative system is I (II) (4) 5.2.4; 

 that is, the rock is transitional between class I, persalane, and class II, 

 dosalane. Placing it with the former, it is again transitional between 

 order 4, quardofelic austrare, and order 5, perfelic canadare. Giving 

 preference to the latter, it falls in rang 2, domalkalic pulaskase, and 

 subrang 4, dosodie larvikose. 



The obvious diiference between the theoretical norm and the actual 

 mode is the presence of hornblende with probably subordinate augite and 

 possibly a shred or two of biotite, whereas diopside and hypersthene are 

 mentioned in the norm. In general we may say that the light-colored 

 components are 87.83 per cent by weight; the dark-colored ones, 11.30. 

 By volume, the preponderance of light-colored would be slightly greater — 

 somewhere about 8 to 1. Orthoclase is in the ratio to plagioclase of 21.13 

 to 55.96, or about 1: 2.5; but alkali feldspar molecules are to anorthite 

 as 65.14:11.95, or about 5.4:1. Quartz diorite porphyry would thus 

 quite well describe the rock, in the ordinary nomenclature. 



In the huge talus of loose rock from the solid laccolith on the south- 

 eastern side of West Butte we have collected many specimens with dark 

 angular inclusions which represent wall rocks of the supply conduit 

 picked up in the passage of the magma upward. Some appear to repre- 

 sent hornblendic gneiss, presumably from the basal Precambrian ; others 

 are dark femic aggregates which may be recrystallized limestones or cal- 

 careous shales. Specimen 2h is a quartz diorite porphyry with an in- 



