part 4] NOKITE OF SIEEEA LEONE. 347 



Discussion. 



Dr. J. W. Eyans expressed his sense of the value o£ this paper, 

 which described an intrusion of norite of unusual size and excep- 

 tional characters. The comparatively fine grain of the main 

 intrusion might be explained by the fact that its present form 

 corresponded approximately to its original contours. The subse- 

 quent intrusions might owe their coarser texture to the fact that 

 the mass into which they were intruded was still hot. It would 

 have been more satisfactory if the contact of the norite with the 

 surrounding rocks could have been investigated by means of 

 borings through the alluvium, but that was impracticable at the 

 present time. 



Mr. A. E. Kit SON" congratulated the Author on the valuable 

 work that he had done in Sierra Leone. He agreed with the view 

 that the norite-mass of the Colony had probably been intruded 

 along a zone of faulting, and thus had determined to some extent 

 the character of the coast-line of this part of West Africa. 



Since the norite-mass had not been foliated, he believed that it 

 was later than pre-Cambrian in age. The remnants of old plat- 

 forms showed strong evidence of at least four successive uplifts, 

 aggregating more than 1000 feet above sea-level. He agreed with 

 the Author that there had been a good deal of assimilation of the 

 older norite by the younger intrusions. Examples of assimilation, 

 though of different rocks, occurred in the Gold Coast. He added 

 that it was interesting to note that, although in the area between 

 Freetown and the Hill Station there was a considerable amount of 

 bauxitic ' laterite,' he had not seen any blocks of bauxite. 



The Author thanked the Fellows present for the kind reception 

 given to the paper, and the speakers for their remarks. With 

 reference to Dr. Evans's observation concerning the coarse texture 

 of the younger intrusions, the Author thought that this texture 

 was accounted for, not only by the fact that the younger norites 

 were intruded into a mass that had not entirely cooled down, but 

 also by the fact that they were themselves probably of considerable 

 size, although commonly giving rise only to small outcrops. Also, 

 when intruded, they had sufficient reserve of heat to incorporate 

 the older rock in considerable amount. Finally, the coarser texture 

 was possibly induced by a slight difference in composition, much 

 as in the case of the succeeding intrusions of norite-pegmatite, 

 which were even coarser in texture. In reply to Mr. Kitson, 

 the Author stated that iron-ores occurred in the younger norites 

 much as in the older norites, except that in the former they were 

 present only as grains and small segregations, and not as schlieren. 

 Also, bauxite occurred in small amount on outcrops of both the 

 older and the younger norites. 



Q. J. G. S. No. 312. 2 b 



