﻿258 



DK. A. HOLMES ON THE TEKXIAKY 



[vol. lxxii, 



Mozambique example. The high silica-percentage of the latter is 

 probably due to the presence in the specimen analysed of small 

 quartz-bearing amygdales, and also to the presence of quartz in 

 the microgranophyric groundmass :— •- 



A. 



D. 



E. 



G. 



EL 



Si0 2 60-76 



Al,6, 16-81 



FeO 



MgO 



CaO 



Na.,0 



K,6 



H."0 



TiO., 



MnO 



P,0, 



2-07 



2- 34 



3- 27 

 6-57 

 3-32 

 2-42 

 1-67 

 0-31 

 0-22 

 n.d. 



51-32 

 16-62 



9-28 



5-36 

 9-62 

 2-15 

 2-96 

 2-60 

 n. d. 

 0-55 

 0-25 



Totals 99-76 100-71 100-48 99-76 100-13 



56-65 

 22-11 



3-31 



3- 42 

 6-67 



1- 86 



4- 10 



2- 20 

 n.d. 

 0-16 

 tr. 



51-97 

 16-21 

 3-37 

 9-51 

 3-68 

 7-67 

 3-41 

 1-75 

 1-97 

 0-22 

 n. d. 

 n. d. 



56-14 

 17-81 



2- 69 

 4-67 

 4-15 

 6-81 



3- 59 

 1-63 

 1-16 

 1-23 

 0-08 

 0-12 



65-32 

 16-08 



2- 13 



3- 47 



4- 33 

 3-62 

 1-06 

 0-17 

 n. d. 

 D.d. 



66-40 

 12-91 

 3-87 

 2-56 

 0-53 



2- 32 



3- 30 



3- 09 



4- 25 

 0-54 

 0-09 

 0-16 



62-07 

 17-15 



1- 87 



3- 57 



2- 39 



4- 84 

 4-75 

 2-15 

 1-18 

 0-21 

 0-26 



tr. 



99-07 100-02 100-44 



1 Including 0-01 per cent. SrO and 0-04 per cent. BaO. 



A. Hornblende-andesite, Monapo River (an. Holmes). 



B. Olivine-augite-andesite, 1 Mount Meru. 



C. Amphibole-biotite-andesite, 2 Mount Meru. 



D. Andesite, Kordofan 3 (an. Linck). 



E. Andesite, near the Lucalla River, Angola 4 (an. Harwoodj. 



F. Base of hornblende-andesite, Monapo River (an. Holmes). 



G. Toscanite, Indulawane Hill, Zululand (an. Prior). 



H. Quartz-porphyry, Kadero, Kordofan 3 (an. Linck). 



Chemical Composition of the Ground-mass. 



The heavy -liquid separation of the ground-mass already men- 

 tioned was not quite clean, for a greater proportion of biotite and 

 andesine accompanied the residue than appeared to be visible in 

 thin section. However, it was thought advisable to analyse the 

 material thus obtained, on account of the light that it might throw 

 •on problems of differentiation. 5 The ground-mass would be expected 

 to have the composition of a latite or rhyolite, and although in 

 Mozambique no such rocks have been discovered in association 

 with the basalts, corresponding dyke-rocks are known to exist at 

 Sinjal in the extreme west of Zambesia, among the volcanic rocks 

 south of the Zambesi and the Lebombo. and in Uganda and 

 Kordofan. 



The separated material was air-dried at 110° C. Owing to 



1 E. Pinkert, Foldt. Kozl. vol. xxxvii (1907) p. 292. 



2 Id. ibid. p. 296. 



3 Neues Jahrb. Beilage-Band xvii (1903) p. 428. 



4 A. Holmes & H. F. Harwood, Min. Mag. vol. xviii (1916) p. 69. 



5 See Sir Jethro Teall, Q. J. Gr. S. vol. Mi (1901) p. lxxxii. for the applica- 

 tion of this method to the rocks of the Cheviots. 



