BY H. I. JENSEN. G 1 3 



columnar grains. It shows a strong pleochroism giving reddish 

 or brownisli-yellovv, wine-yeliow and very pale yellow. Irregular 

 cracks in a direction transverse to the length of the prisms 

 sometimes occur. A cleavage, and occasionally twinning, may 

 be noticed running in the direction of the length of the crystals. 

 The extinction angle varies from 0° to 20°. Double refraction 

 is strong. From these characters, the mineral, which forms 

 about 10% of the rock, appears to be laavenite. Next in order 

 of abundance we liave minute prisms, grains and lozenge-shaped 

 microlites, clear colourless sphene with characteristic high refrac- 

 tive index and double refraction. A light greenish to colourless 

 diopside also occurs in grains. Melilite occurs in patches and is 

 moulded on the felspar enveloping it in an ophitic manner. It 

 has the characteristic peg-structure. Finally we have an 

 isotropic colourless interstitial substance which gelatinises with 

 acid; it probably consists of leucite or anal cite. 



4. Order of consolidation : 

 1 . Sphene 



2. Felspar (2nd gen.) 



3. Corundum (1) 



4. Laavenite Q) 



5. Melilite 



6. Isotropic base 



A little primary haematite is present, and crystallised out 



early. The felspar of the first generation was highly corroded 

 by the magma just before the period of crystallisation. A ferro- 

 magnesian mineral (either an amphibole or pyroxene) was also 

 original^ present but was completely resorbed, and one can 

 only trace its former presence by the existence of patches of 

 dusty corundum and magnetite and isotropic mineral, which 

 have the outline of hornblende phenocrysts. The orginal mineral 

 has been completely pseudomorphosed. 



The chemical composition of the rock is so extraordinary that 

 one can only account for the amount of FcoOg by assuming that 

 the black mineral is, in part at least, garnet. In this way the 



