218 SCIENCE PROGRESS 



deposited. Vanua Levu has batholithic gabbro, followed, 

 after erosion, by lavas and volcanic ash. The Lau Islands 

 consist of volcanic rocks and limestone. 



The rocks of the Reefton Subdivision of New Zealand con- 

 sist of sharply folded greywackes and argillites, probably of 

 Lower Palaeozoic age, overlaid first by Devonian, then by 

 Tertiary rocks of Eocene and Miocene age. The older rocks 

 have been invaded by granitic intrusions. The economic 

 products are gold-quartz veins, alluvial gold gravels and con- 

 glomerates, and coal. 



Petrology 



Sederholm, J. J., On Synantectic Minerals and Related Phenomena, Bull. 



Comm. Geol. P/nlande, 1916, No. 48, pp. 148. 

 Calkins, F. C, A Decimal Grouping of the Plagioclases,/. Geol. 1917, 25, 157-9. 

 IDDINGS, J. P., and MORLEY, E. W., A Contribution to the Petrography of the 



Island of Bawean, Netherland Indies, Proc. Nat. Acad. Set. {Wash.), 1917, 3, 



105-9. 

 Holmes, A., Picrite from the Ampwihi River, Mozambique, Geol. Mag. (6), 191 7, 



4, 150-7. 

 Tyrrell, G. W., Trachytic and Associated Rocks of the Clyde Carboniferous 



Lava-Plateaus, Proc. Roy. Soc. Edin. 191 7, 36, pt. 3, 288-99. 



Sederholm 's work on synantectic minerals deals with 

 structures such as reaction-rims, corona-minerals, kelyphite, 

 myrmekite, etc., found in igneous rocks and occurring at the 

 mutual boundaries of minerals. These mineral associations 

 are termed synantectic. The structures are believed to be of 

 primary igneous origin in granitic rocks, but are referred to 

 the last stages of consolidation when residual fluids and gases 

 played an important part. In the mafic rocks synantectic 

 structures are believed to be of secondary or metamorphic 

 origin. 



Calkins has constructed a diagram showing the surprising 

 diversity of usage of various authorities in subdividing the 

 range of the plagioclase felspars. He proposes a decimal 

 grouping, so that the term albite covers the range from Abioo 

 to Ab 90 ; oligoclase, Ab 90 — Ab 70 ; andesine, Ab 70 — Ab 50 ; labra- 

 dorite, Ab 50 — Ab 30 ; bytownite, Ab 30 — Ab 10 ; and anorthite, 

 Abio — Ab . This seems to be a sensible and useful suggestion. 



The rocks of Bawean, described by Iddings and Morley, are 

 highly alkalic and potassic lavas which belong to vicoite and 

 phonolite. One of the vicoites falls into a hitherto unnamed 



