304 DE. r. DiXEY ox THE [vol. Ixxviii, 



of the Colony ; inland, Avhere the bush is verv dense, they rarely 

 crop out elsewhere than in stream-beds and as joint-faces along the 

 sides of valleys. The various rock-types will be described below 

 in their order of intrusion, namely : — 



(i) Older or normal norite. 



(ii) Yoimger norites and norite-pegmatite. 

 (iii) Beerbachite. 

 (iv) Xorite-aplite. 



(v) Dolerite. 



(5) Age of the llocks. 



Although no field evidence has been found to throw any certain- 

 light upon the age of the complex, there are many considera- 

 tions of a general character which indicate that.' while probably 

 later than pre-Cambrian, it is nevei'theless of very great age. 

 The only rocks seen in contact with the complex are the- 

 Pleistocene sediments which rest upon it on all sides, and the- 

 nearest rocks of an earlier age than these are representatives of an 

 ancient series of crystalline schists and gneisses which are exposed 

 in the Port Lokko Creek, 11 miles east-north-east of the north- 

 western end of the norite-complex. Since the complex is elongated 

 in a direction parallel Avith the general trend of the coast of this 

 part of West Africa, it is obvious that few, if any, rocks will b& 

 exposed on the strike, or on the seaward side, of the complex.. 

 The only crystalline rock known to occur actually on the strike of 

 the complex is the nepheline-syenite of the Los Islands, situated 

 off the coast of French Guinea at a distance of 72 miles fi*oni 

 Freetown ; it is important to notice, however, that the mainland 

 opposite the Los Islands consists of a series of diabases, gabb:^s, 

 and peridotites intruded into ancient crystalline schists.^ In the 

 Protectorate of Sierra Leone, crystalline rocks approach the strike 

 of the complex in the locality already mentioned, and also in the- 

 mamland oif the noith-eastern comer of Sherbro Island. Thus it 

 is seen that all the old rocks exposed on the strike, and on the 

 landward side, of the norite, over a large area extending from 

 Liberia to the Los Islands, belong to an ancient series of 

 crystalline schists and gneisses generally considered to be of 

 pre-Cambrian age.~ The following considerations show that the 



^ A. Lacroix, • Les Syenites Xepheliaiques de rArchipel de Los " Xony. 

 Arcli. Mus. Hist. Xat. Paris, ser. 5, vol. iii (1911) p. 108. Xote, moreover, 

 that along the coast of Liberia there are at least fonr masses of g-abbro and 

 associated basic rocks -n-hich are largely similar in occurrence to the norite of 

 Sierra Leone, but of smaller size. See also H. Hubert, • Carte Geologiqne 

 de I'Afrique Occidentale' 1920, and Delafosse, 'Le Liberia en 1907' pt. ix : 

 Geologie. Bnll. Com. Afriqne Franc. 1907, Xo. 12. 



- See A. E. Kitson, 'The Gold Coast : some Considerations of its Structare,. 

 People, & Xatnral History ' Geogr. Jonrn. vol. xl-rai (1916) p. 377 ; id. • Out- 

 lines of the Geology of Southern Xigeria (British "West Africa), with especial 

 reference to the Tertiary Deposits ^ Abs. Proc. Geol. Soc. 1918-19, pp. 100- 

 105. Also J. D. Falconer, ' The Geology & Geography of Xorthem Nigeria ' 

 1911. and ' The Geology of the Plateau Tin-Pields ' Bull. Xo. 1. Geol.'Surv. 

 Nigeria (1921) p. 33. 



