342 DE. F. DIXEY OX THE [vol. IxXYUl,. 



of the dolerite. Also, inicrograpliic structures are abundantly 

 developed in the felsj)ar, and granules of augite run along its 

 boundaries. The pyroxenes and the olivine all show more or less 

 complete recrystallization, and they are, moreover, granulated 

 around their maro-ins ; the STanules alono- the maro'ins of each 

 mineral ai-e intermixed with those of the other minerals, and also 

 with flakes of biotite. 



In conclusion, I wish to express my thanks to Prof. A. H. Cox, 

 of the University College of South AVales & Monmouthshire,. 

 Cardiff, to whom I am indebted for many valuable suggestions in 

 the course of this work and also for laboratory accommodation 

 during the examination of specimens. 



IT, Sl'm:maet axd Coxclusioxs. 



(1) The norite of Sierra Leone constitutes a complex, of which 

 the oldest and most important member is an olivine-norite. The 

 complex forms the mountainous mass which, together with a 

 narrow coastal plain of Pleistocene sediments, makes i\p the Sierra- 

 Leone peninsula. 



(2) The norite differs from other well-known noritic intrusions 

 in its great size, apparent batholithic character, and lack of exposed 

 marginal or basic phases ; its junction Avith older rocks is obscured 

 b}'' the Pleistocene sediments. 



(3) The complex is believed to be of very o-j-eat age, although 

 probably later than pre- Cambrian ; it belongs to the AYest African 

 Magnesian Province. 



(4) The main intrusion of norite was invaded in succession by 

 the following related minor intrusions: — (i) norites of slightly 

 different character, which generally possessed a coarser texture ; 

 (ii) norite-pegmatite ; (iii) beerbachite ; (iv) norite-aplite ; (v) 

 dolerite. 



(5) The first intrusion of norite consists essentially of labra- 

 dorite, augite, and hypersthene, with varying ])roportions of olivine 

 andiron-ore (titanomagnetite). The rock is beautifully fresh, and 

 it o'enei-allv exhibits stiono- flow-bandino-. In addition to the 

 intrusions already mentioned, the older norites are cut by segre- 

 gation-veins, by veins emanating from the younger norites, and by 

 small lenticles of a felspar- olivine rock, 



(6) An interesting series of binary and ternary intergrowths of 

 the common minerals has been observed in the norite, indicating 

 the importance of eutectic conditions during the crystallization 

 of the magma. Consequently, there was very often no regular 

 order of crystallization among the principal minerals. 



(7) The younger norites form two or more series of intrusions 

 cutting the older norite ; but they are collectively of small bulk 

 as compared with the original intrusion. In addition to their 

 g^reater coarseness, they are as a rule readily distino-uished in the 

 field from the older norite by their grey colour and scaly weathered 

 surface, and also by the absence of banding and jointing. In thin 



