BY H. I. JENSEN. 89 



The analysis computed in accordance with the American 

 system gives the following norm — 



Per cent. Per cent. 



Quartz 17-58 Magnetite 1-16 



Orthoclase 25-02 Ilmenite 1-22 



Albite 50-83 Haematite 064 



Anorthite 1-85 Water 1-09 



Corundum 1-12 



The rock therefore falls in Class i., Subclass i., Order 4, Rang 1, 

 Subrang 4. 



Magmatic name : Kallerudose. 

 Name : Porphyritic Soda-Trachyte. 



F1.12. A dark grey rock containing white fragments of 

 trachyte-porphyry. The dark portion is a microcryptocrystalline 

 to glassy lava which, under the high power, is seen to consist 

 partly of crystallites, globulites, margarites and spherulitic tufts 

 of crystallites. 



The phenocrysts are idiomorphic and somewhat corroded. 

 They are interesting as exhibiting in an excellent way the cause 

 of the shadowy extinction of anorthoclase. Some crystals are 

 composed of orthoclase and albite in parallel growth, each felspar 

 being quite distinct. Others, in which the intergrowth is finer, 

 must be classed as inicroperthite. In others again the extinction 

 of the felspars is shadow}-, but there is no evidence of intergrowth 

 until the crystal is turned almost to the position of extinction, 

 when it becomes faintly cross-hatched. Doubtlessly the shadowy 

 extinction of anorthoclase, whether primary or induced by strain, 

 is due to the interlaraellation of two felspars and ultramicroscopic 

 twinning in the plagioclase component. 



All the rocks hitherto discussed are decidedly acid. They yield 

 poor sandy grey soils. 



2. Trachytes — (6) The True Trachytes. 



Fl A. Lava from the summit of Mt. Flinders. 



Handspecinien : greenish-grey rock, mottled like "mackerel 

 sky," and consisting of dark greenish areas intergrown with light 

 greenish areas. Macroscopically ver}'^ fine-grained. 



