Prof. S. J. Shand — IVie Norite of the Sierra Leone. 21 



Plate IV. 

 Fig. 



10. Valuta (Pyrgomitra) fusus (Philippi), p. 410. Mus. Ipswich. 



11. Conus aiitediluviamis, var.,Grateloup, p. 410. Mus. Pract.Geol. London. 



12. Pleurotoma Steinvortlii, Semper, p. 410. Mus. York. 



13. Natica ferrugitiea, var. (in Sacco), p. 414. Mus. Ipswich. 



14. Calliostoma Xavieri {Costa M.S.), Tp. 4:15. Mus. Ipswich. 



15. Nucula placentina, Lamarck. Mus. Ipswich. 



16. Astarte Kickxii, Nyst., p. 417. Mus. Pract. Geol. London. 



17. Cardium Woolnoughi, n.sp. 17a shows the sculpture as seen in the 



intaglio or hollow mould. 176, inner mould of organism with the shell 

 removed by decalcification. Mus. Pract. Geol. London. 



18. Cyrtodaria vagina (S. V. Wood). Mus. Pract. Geol. London. 



19. Flabellum cuneatum [Goldiins,?,). Bell Coll. 



IV. — The Norite of thij; Si'keea Leone. 

 By Professor S. J. Shand, D.Sc, F.G.S., University of Stellenbosch, South 



Africa. 



rPHE Sierra Leone, from which, the Colony of Sierra Leone takes 

 X its name, is a range of palm -covered hills running parallel to 

 the coast (N.N.W.-S.S.E.). It is truncated on the north by the 

 wide mouth of the lloquelle (Kokell) River, which forms the 

 magnificent harbour of Freetown. Towards the south the range 

 terminates at Tawry Bay. The length of the Sierra is therefore 

 about 25 miles and its width, from Kassa Town to Kissy, 

 about 8 miles. On the east side the range descends steeply to the 

 Kwaia plain, from wliich it is separated by Waterloo Creek. The 

 detachment of the hills from the interior lowland is sufficiently 

 complete to entitle one to speak of the Sierra Leone Peninsula. 

 Freetown is built on the north end of the peninsula, overlooking the 

 harbour, and it straggles up from sea-level to a height of some 

 800 feet on Wilberforce Hill. The greater part of the peninsula is 

 covered with thick tropical vegetation right down to sea-level ; and 

 an additional obstacle to geological study is created by the heavy 

 covering of laterite which screens the rocks from observation. In 

 places this laterite mantle is 30 feet tliick. But along the northern 

 shore of the peninsula, from Cape Sierra Leone to the mouth of 

 Waterloo Creek, there are nearly continuous exposures of norite, 

 and further useful exposures liave been made during the construction 

 of the Hill Railway and along certain of tlie roads on the hillside. 

 These outcrops make it clear that the whole of the north end of the 

 Sierra is formed of norite, and it would not be surprising to learn 

 thiit tlie entire Sierra has the same composition. 



The norite or gabbro of Freetown was described by G. GUrich in 

 1887,' and I have not been able to trace any subsequent reference to 

 it. Rocks from the interior of tlie colony were examined by G. F. 

 Scott Elliot and Miss C. A. Raisin in 1893,^ and as far as I am aware 

 no further contribution to the geology or petrology of the country 

 has been made since that date. I spent a few days in Freetown 

 recently, and took advantage of the opportunity to examine the rocks 

 and collect a few specimens. I can add little to the account of the 



' Zeit. der Deutschen Geologischen Gesellschaft, vol. xxxix, p. 108. 

 '^ Colonial Eeports, Misc., No. 3 (Sierra Leone), p. 61. 



