400 



I. Dacite from Mojanda, Quito. Order of separation : magnetite and apatite, 

 hornblende, plagioclase, quartz, hornblende-microlites, felspar and quartz (?) of the ground- 

 mass. The presence of base is doubtful. 



II. Ground-mass of the above rock. 



III. Zonal plagioclase from the above rock. Composition lies between Ab4, Ans and 

 Abi, Am. Extinction on M - 12 ; on P - 3. 



IV. Trachyte, Mte. Amiata, Tuscany. Order of separation : magnetite and apatite, 

 augite, mica, plagioclase, sanidine, microlites of the ground-mass. 



V. Glassy globulitic base of the above rock. Contains pores in which tridymite occurs. 



VI. Sanidine from the above rock. The sanidine separated after the augite, mica and 



plagioclase when the molten portion of the rock had the following composition according to 



LAGOEIO: Si0 2 69-88; Al 3 O 3 + Fe 2 O3, 17'30; CaO 0'71; K 2 778; Na 2 2-22.U) The ratio of 



K 2 O : Na 2 is therefore 2-3 : 1, and that of K 2 + Na 2 : SiO 2 , 1 : 9-82. 



VII. Andesite from Hliniker Thai, Hungary. Order of separation : magnetite and 

 apatite, mica, hornblende, augite, plagioclase, spherulitic bodies in the base. 

 VIII. Isotropic base of the above. 



IX. Plagioclase of the above. Abi, Am. 



X. Vitro-andesite. Block ejected from Merapi, Java. Order of separation: magnetite 

 and apatite, augite, plagioclase ; then magnetite, augite and felspar-microlites in the base. 



XI. Glassy base of the above. 

 XII. Plagioclase of the above, Abs, Am. 



These analyses all point to the conclusion that the effect ot 

 progressive crystallization in an andesitic magma is to increase the 

 percentages of silica and alkalies, especially potash, and to diminish 

 the percentages of lime, iron and magnesia in the mother liquor. 

 In short, the mother liquor approximates in composition to a mixture 

 of quartz and orthoclase. 



I. Vitro-basalt from Schwarzenfels, Rhim. Order of separation : oliviiie, augite, 

 plagioclase. 



II. Glassy base of the above rock. The ratio of K 2 : Na^O is slightly greater in the 

 glass than in the rock ; 1 : 5' 2 as against 1:6. 



III. Dolerite, Mont Dore. Order of separation : magnetite and apatite, olivine, 

 augite, plagioclase (bytownite). 



IV. Glassy base of same rock. In glass K 2 : Na 2 = l : 2 ; in rock K 2 : Na 2 0= 

 1 : 2-5. 



V. Limburgite, Kaiserstuhl. Order of separation : magnetite, hyalosiderite, augite, 

 microlites of the base. 



VI. Glassy base of the same rock. KjO : Na 2 = l : 1-3 in glass and 1 : T25 in rock. 



(1) These numbers are not reckoned so as to express the percentage composition, but only 

 the relations of the different constituents. 



