270 



SCIENCE PROGRESS 



the Quantitative Classification of Igneous Rocks, 1903 ed., be 

 rapidly carried out. 



Dr. Washington has had forms printed on cards to facili- 

 tate the calculations required for determining the place of a 

 rock in the classification. On one side is the analysis, with the 

 molecular proportions to three places of decimals ; on the other, 

 the calculations and classificatory results. He very kindly sent 

 me some of them filled in with the particulars of the rocks from 

 the River Madeira. The results he obtained for the rock already 

 referred to were as follows : 



Quartz 

 Orthoclase . 

 Albite 

 Anorthite 

 Corundum . 



Hypersthene 



Magnetite, etc. 



/FeO.Si0 2 \ 

 iMgOSiO,/ 



Percentages 

 by weight. 



31-26 

 30'02 s 



29-87 



3-6i j 

 •41 



48 



63-50 



2'4») 

 ri6i 



95'i7 



• 3*64 



98-81 



This is practically the same result as that given above, 

 though by a curious accident the orthoclase and albite are 

 almost exactly interchanged. 



Results of the Classification 



Rocks classed as Liparose by Dr. Washington x had been 

 previously described as granite, granitite, hornblende granite, 

 soda granite, aplitic granite, aplite (haplite), lithionite granite, 

 quartz syenite, quartz lindoite, granophyre, porphyry, granite- 

 porphyry, Rapakivi granite and granite-porphyry, quartz 

 porphyry, quartz tourmaline porphyry, quartz syenite-porphyry, 

 syenite-porphyry, felsite-porphyry, bostonite, keratophyre, 

 quartz keratophyre, rhyolite, rhyolitic glass, obsidian, rhyolite- 

 obsidian, pitchstone, trachyte, quartz pantellarite, nevadite, 

 liparite, dacite, andesite-obsidian, andesite (decomposed), 

 comendite, paisanite, alaskite, and arfvedsonite grorudite. 



This long list of names is accounted for to some extent by 



the differences of structure and mineral composition resulting 



from varying conditions of consolidation. The indefiniteness, 



confusion, and redundancy of modern nomenclature are also 



1 See Che}nical Analyses of Igneous Rocks, supra cit., pp. 144-53. 



