Y6 V<']. Xl.III., Art. e. — S. Ts-.iboi : 



The subordinate phenociysts are of hypersthene, rather low in 

 FeO as may be inferred from its optical properties, and of light 

 greenish augite, snbhedral to anhedral and prismoid to equant, 

 •sometimes twinned after (100). The two are found in some cases 

 in parallel intergrowth. Their optical properties are : — 

 Hypersthene 



6!<1.G906<^5<1.7146<;' 

 2Z?rrr89° 2F==8'2° supposing ,5 — 1.7 Optical character .... negative. 



Pleochroism : — 



A^. . . .light reddish bvown 

 Y . . . .light reddish yellow 

 Z . . . . light bluish green 



Alt (J it e 



«< 1.6869 1.6869<;9< 1.6906 1.7{)14<r cA/f=45° 



The angle cAZ was measured on a section of augite in parallel 

 intergrowth with hypersthene whose interference figure shows that 

 the section is cut parallel to (010). 



The intersertal (jroiniclmass consists of plagioclase prisms, 

 0.05 — 0.3 nmi. in length, light greenish augite grains ('>:< 1.6836 <i5 

 <1.6869</'), and magnetite, subhedral to anhedral often showing 

 -dendritic skeletal crystals. 



4) Hypersthene -bearing augite-olivine-bytownite-basalt. 



(Ti>c fourth type of tlio .-omnia lava.) (PI. II. Fig. 4.) 



Kock of this type is highly characterized by the presence of 

 abundant olivine phenocrysts, and is decisively distinguishable from 

 the preceding types in this respect. 



3Io(le of Occurrence. — This type is a decidedly rare one, oc- 

 -curring only at the locality indicated on tlie geologic map (PI. V. 



