﻿248 



DR. A. HOLMES ON THE TERTIARY 



[vol. lxxii r 



Chemical Composition. 



The Sokoto-Hill and Mochelia basalts were analysed with the 

 results tabulated below. The analysis of the former rock was 

 made under my direction by my former students, Lieut. J. L. 

 Harris, M.C., the late Lieut. Gr. Kirby, and Mr. E. Spencer : — 



Sokoto Hill. 128. 



Molecular 

 Percentages. Proportions. 



SiO, 52-42 -874 



Al 2 6 3 17-40 -171 



Fe~,0., 4-21 -026 



Feb.' 5-16 , -072 



MgO 5-30 -132 



CaO 9-08 -163 



Na.,0 2-65 -043 



K,6 1-77 -018 



1L"0 1-26 



TiO., 0-67 -008 



MnO 0-24 -003 



Total 100-16 



Molecular 

 Percentages. Proportions. 



SiO., 51-21 -854 



A1,0 3 17-99 -176 



Fe~6, 4-63 -029 



FeO." 5-81 -081 



MgO 6-11 -153 



CaO 9-36 -167 



Na.,0 2-92 -047 



K.,0 1-03 -011 



H,0 + 0-32 



H 2 0- 0-72 



TiO, 0-42 -005 



P.,0", tr. 



MnO 0-27 -004 



Mineral Composition 





(Norm). 



Quartz 



3-75"! 





Orthoclase 



10-01 1 



Salic 



Albite 



22-53 



^=66-87. 



Anorthite 



30-58^ 





Diopside 



12-10^ 





Hypersthene 



. 12-66 1 



Femic 



Magnetite 



6-05 



^=32-03.. 



Ilmenite 



l-22_, 







98-90 





Water 



1-26 





Total 



100-16 





Mineral Composition 





(Norm). 





Quartz 



0-991 





Orthoclase 



6-12 { 



Salic 



Albite 



24-63 f 



= 64-54.. 



Anorthite 



32-80 J 





Diopside 



10-96"] 





Hypersthene .. 



. 16-75 \ 



Femic 



Magnetite 



6-73 f 



= 35-20. 



Ilmenite 



0-76 J 







99-74 





Water 



1-04 





Class II Dosalane. 



Ra=0 - 98 X 10~ 12 grms. per grm. Order 5 Germanare. 



Specific gravity=2-70. Rang 4 Hessase. 



Subrang 4 ... Hessose. 



Mochelia, 141. 



Total 100-79 Total 100-78 



Class H Dosalane. 



Ea=0-85xl0~ 12 grms. per grm. Order 5 Germanare. 



Specific gravity = 2-72. Eang 4 Hessase. 



Subrang 4 ... Hessose. 



For comparison, the analyses are repeated below with others of 

 the same type. The occurrence of a similar basalt in Somaldand 1 

 is interesting, for it preceded the eruption of a series of alkali 



1 A.de Gennes & A. BonarcL C. E>. Acad. Sci. Paris, vol. cxxsi (1900) p. 196. 



