78 "^'ol. XLIÎI., Art. G. — S. TsnbM : 



are seon abundantly. They are generally subhcdral, commonly 

 twinned according to the Carlsbad, albite, and rarely pericline laws, 

 and carry ratîier abundant inclusions (mostly augite grains,- ex- 

 tremely few magnetite crystals, and a fine dusty substance), usually 

 arranged zonally in thin bands parallel to the crystal outline. Tlie 

 zonal structure due to chemical différence is sometimes exhibited, 

 especially in the psripheral part, though very faintly. In the 

 simplest case, the less calcic plagioclase surrounds the more calcic, 

 but in somo cases the more calcic and less calcic zones alternate 

 between tlie most calcic core and the least calcic outermost shell. 



Phenocrysts of o^.wlm, next to those of plagioclase in amount, 

 are anhedral to subhedral, generally resorbed, often with deep 

 indentation. The alteration products, iddingsite and magnetite, are 

 often seen deposited along the cracks. Very poor inclusions of this 

 mineral are colourless glass and trichites. 



Subordinate phenocrysts of pyroxenes, of which hyperstJiene is 

 negligible in quantity, show the usual characters. Of the augite 

 phenocrysts the following refractive indices were measured'-*: — 

 a':^1.686D l.G8r.9<:,5< 1.6906 1.7014<j' -/< 1.7168 



The groimdmass is psrcrystalUne, centimillimeter-grained, and 

 granular intersertal, being built up of granular augite and prismoid 

 plagioclase with euhedral magnetite scattered here and there and 

 only a negligible amount of glass, very often appearing brown bo- 

 cause of fine dusty inclusions. It is a remarkable feature of the 

 groundmass that the mafic components nearly equal, and at times 

 even exceed the felsic, in quantity as well as in size. 



Name of Mock — The present rock is so rich in olivine that it 

 is inferred to belong to the perfelic order of the quantitative system. 



indicfs 



1) Here a' aud 7' denote respectively (lie obse:ved minimum and maximum refractive 



