IV.—The Norite of the Sierra Leone

Extract

The Sierra Leone, from which the Colony of Sierra Leone takes 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 Roquelle (Rokell) River, which forms the magnificent harbour of Freetown. Towards the south the range terminates at Yawry 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 which 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 riglit 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 thick. 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 have been made during the construction of the Hill Railway and along certain of the 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 that the entire Sierra has the same composition.