BY H. I. JENSEN. 



'07 



The calculation of the norm of this rock resulted as follows 



Orthoclase 



Albite 



Anorthite 



Diopside 



Olivine 



Hjematite 



Magnetite 



Ilmenite 



Water 



Total 



44-89 _^ 5^ 8 



Fern." 55 00 """^3 ^5 



Sal. 



] 

 hence salfemic. 



Felspar 44-89 ^ 7 

 Quartz ~" ^T 



hence Order Gallare. 



K20 + Na.30 _ 59 ^ 3^ 1 

 ' CaO "179"^ 5^^y 



hence Docalcic. 



K^O _20^3^ 1 

 Na20~39^5^7 



Magmatic name : Auvergnase. 



The comparison of the analysis and norm with the petrological 

 description was of some interest. 



The analysis bears out my statement that the augite is titani- 

 ferous, for the ilmenite actually present in the rock is much below 

 that which we should expect if all the titanium had gone to form 

 ilmenite. My conclusion that the haematite present is a primary 

 constituent also follows from the norm. The felspar, however, 

 as calculated from the norm, differs totally from the felspar as 

 observed in the slide. 



From the norm we should expect the dominant felspar to be a 

 variety of andesine, but my examination of the rock-slide revealed 

 only basic labradorite or bytownite. This might be accounted 

 for through two circumstances; first, the existence of a glassy 

 residuum which may be very acid in composition; second, the 

 fact that the augite is greenish-brown and highlj^ pleochroic, 

 which phenomena suggest richness in alkali, especially soda. 



After the analyses had revealed this disparity between the 

 norm and the mode, as previously obtained, the rock was again 

 examined under the microscope. The description already given 

 in the paper referred to was found to be essentially correct. 



