7IO PETROLOGICAL ABSTRACTS AND REVIEWS 



augite, magnetite, rare apatite, and negligible glass in the gray varieties, and 

 plagioclase and augite in brown glass in the slaggy kinds. Five chemical 

 analyses are given, all giving high SiO^ (51.94, 5i-i3, 5i-32, 5i-40, and 51.45). 

 The rock is given a new name on account of its occult quartz and normative 

 bytownite. Mineral percentages are not given. 



TsuBOi, Seitaro. "A Diagram for Determining Plagioclases." 

 Published in the Japanese language in Jour. Geol. Soc. Tokyo, 

 XXVII (1920). 



Since cleavage pieces of plagioclase are used in determining their refractive 

 indices, a table giving the values in (010) and (001) is of much greater value 

 than the usual one giving a, /3, and 7. These values, computed by Tsuboi 

 and plotted as a curve, are reproduced in the reviewer's Essentials in the Deter- 

 mination of Rock-forming Minerals and Rocks. 



Tsuboi, Seitaro. "On a Leucite Rock, Vulsinitic Vicoite, from 

 Utsuryoto Island in the Sea of Japan," Jour. Geol. Soc. Tokyo, 

 XXVII (1920), 91-104. 



Describes a porphyritic rock with abundant phenocrysts of sanidine and 

 labradorite, the former slightly more abundant than the latter, less hornblende, 

 augite, and titanaugite, and microphenocrysts of biotite, olivine, and apatite. 

 The groundmass consists of laths of orthoclase and plagioclase and round leu- 

 cites, with prisms and grains of aegirite-augite, some magnetite, and a trifle 

 glass. An analysis is given which, recast into the norm, gives 4.63 per cent 

 nephelite, 39.59 orthoclase, but no leucite. The analysis is readjusted to give 

 leucite with the approximate proportions orthoclase 21.5, albite 42, anorthite 

 9, leucite 14, diopside 4.5, magnetite 2.8, ilmenite 1.2, apatite i.i, olivine 2.7, 

 and zircon o.ii. Compared with the description, however, this does not 

 represent the actual mode (in which the plagioclase is stated to be labradorite), 

 consequently it cannot be classified in the reviewer's system. 



Tsuboi, Seitaro. "Volcano Oshima, Idzu," Jour. Col. Sci., Tokyo, 

 XLIII (1920), art. 8. Pp. 148, 24 photomicrographs on 4 plates, 

 map I, plate profile i, figs. 42. 

 Part of this report was published in the preliminary papers described in the 

 second and third preceding articles. Here is given a geological and historical 

 sketch of the volcano Oshima as well as descriptions of the rock types. These 

 are basaltic bandaites, miharaites (which resemble the preceding but have no 

 oHvine), and basalt. Various analyses are given, and some beautiful photo- 

 micrographs. 



