part 4] THE JsroEiTE of sierba leo]S'e. 301 



mountain -mass of the Colony. ^ Moreover, during the examination 

 iseveral features of considerable interest were observed, including 

 the assimilation of one phase of the norite by another, the well- 

 . developed banding in the norite, the segregation of the iron-ores, 

 .and the sequence of the minor intrusions. These features, together 

 with an important series of intergrowths of the common minerals, 

 will be described in the course of this paper. The investigation 

 into the mineral resources of the Colony, with especial reference to 

 the iron-ores, formed part of the work of the Greological Survey 

 •of Sierra Leone during the latter part of 1918 and during 1919, 



(2) Physiography of the Area.^ 



The Colony is a mountainous peninsula adjacent to the undu- 

 lating low ground which forms the southern part of the Protec- 

 torate. Its mountains rise steeply from a narrow coastal plain 

 to a height of nearly 3000 feet ; this plain is continuous with that 

 •of the mainland, and is due to a Pleistocene uplift of a little 

 over 300 feet.^ It is made up of marine deposits derived largely 

 from the denudation of the mountains. (See PI. XVI, fig. 1.) 



The mass of the Colony has been carved by erosion from an 

 elongated stock of norite. As now exposed, the stock is 24 miles 

 long and 8 miles wide, but it was doubtless much greater originally. 

 From the southern end of the mass, the Banana Islands (forming 

 .a part of the same intrusion) extend away to the south- south-west. 

 In the course of erosion a number of platforms have been carved 

 into the mountain-mass. The more important of these platforms 

 attain maximum altitudes of about 2400, 1800, and 1300 feet 

 respectively ; they can all be distinguished without difficulty from 

 the summit of one of the higher peaks of the northern end of the 

 'Colony, such as Leicester Peak, and also from the sea a few miles 

 west of Freetown Harbour. The highest platform can be seen 

 :at a level slightly below the summit of Sugarloaf Mountain (see 

 PI. XVI, fig. 1), the second slightly below that of Leicester Peak, 

 while the third forms the high ground that encloses Freetown 

 on the south-east, south, and south-west. The oldest platform 

 forms the upper limit of the broad middle ridge that traverses the 

 'Colony from end to end, whereas the second platform is recognized 

 principally in the even tops of the two lateral ridges that run 

 parallel with the main ridge ; the third platform can be traced at 

 intervals around the flanks of the higher platforms. Several 



^ The term Colony refers to tliat part of Sierra Leone which lies along 

 -the coast ; it forms principally a peninsula about 25 miles long- and 9 miles 

 wide. At the northern end of this peninsula is situated the port of Freetown. 

 The remaining" part of the country is known as the Protectorate; it 

 .extends inland for a considerable distance, and covers an area almost as 

 large as Ireland. 



'^ See also F. Dixey, ' The Physiography of Sierra Leone ' Geogr. Journ. 

 vol Ix (1922) p. 41. 



^ See F. Dixey, ' Pleistocene Movements in Sierra Leone ' Trans. Geol. Soc. 

 S. Africa, vol. xxii (1920) p. 112. 



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