part 4] THE NOEITE OF SIEREA LEO^E. 299 



11. Tlie NoRiTE of SiEEEA Leone. By Feaistiv Dixey, 

 D.Sc, F.G.S. (Bead June 22nd, 1921.) 



[Plates XVI-XIX.] 



Contents. 



Page 

 I. Introduction : 299 



(1) General Remarks. 



(2) Physiography of the Area. 



(3) Size and Form of the Occurrence. 



(4) The Intrusions. 



(5) Age of the Rocks. 



(6) Relation to other West African Basic Rocks, and also 



to a West African Magnesian Province. 



IT. Field Observations 307 



(1) The Older or Normal Norite. 



(2 a) The Younger Norites and Norite-Pegmatite. 



(2 6) Field Relations of the Older and Younger Norites. 



(3) The Beerbachite. 



(4) The Norite-Aplite. 



(5) The Dolerites. 



(6) Differentiation and Assimilation. 



(7) Weathering and Lateritization of the Norite. 

 (8 a) Iron-Ores in the Norite. 



(8 h) Other Economic Minerals. 



III. Petrographical Notes 322 



(1) The Norite-Aplite. 



(2) The Dolerites. 



(3) The Minerals of the Complex. 



(4) Intergrowths of the Common Minerals, and Crystalliza- 



tion of the Norite-Magma. 



(5) The Order of Crystallization. 



(6) Contact- Metamorphism within the Complex. 



IV. Summary and Conclusions 342 



I. Ijs^teoductiois^. 



(1) General Remarks. 



The norite of Freetown (Sierra Leone) was briefl}^ described by 

 O. aiirichi in 1887, and in 1918 Prof. S. J. Shand^ translated 

 Griirich's work, adding a few notes. I had the opportunity of 

 making a detailed examination of this norite, as part of an investi- 

 gation into the mineral resources of Sierra Leone ; and in the course 

 of this work it was found that the norite exposed around Freetown 

 was only one end of a huge noritic complex which made up the whole 



^ ' Olivingabbro von Freetown (Sierra Leone) ' Zeitschr. Deutsch. Geol.. 

 Gesellsch. vol. xxxix (1887) p. 108 ; further reference to this paper will be 

 made below, p. 305. 



2 ' The Norite of the Sierra Leone ' Geol. Mag. 1918, p. 21. 



Q. J. G. S. No. 312. T 



