344: • UK. F. DixEr ox THE [vol. Ixxviii^ 



EXPLAXATIOX OF PLATES XYI-XIX. 



Plate XVI. 



Fig. 1. The Sierra Leone Mountains, looking southwards from the 

 summit of Leicester Peak. The photograph shows part of the 

 middle ridge of the mountain-mass ^vith Sugar-Loaf Mountain, 

 capped by a cloud, on the right. Eegent village is seen in the 

 upper part of the Orugu Valley on the left of the photograph. (See 

 p. 301.) 

 2. Contact of coarse norite with older or normal norite, 

 foreshore, near Ciodrich. The left-hand portion of the photograph 

 shows normal norite, easily recognized by its jointing : in the right- 

 hand portion is seen part of a big intrusion of coarse norite, charac- 

 teristically free from jointing. (See p. 310.) 



Plate XVH. 



ig. 1. Coarse norite invading normal norite, foreshore, near York. 

 The photograph shows fragments of normal norite embedded in 

 coarse norite. The fragments, recog-nized by a relatively- smooth 

 weathered surface, possess deeply corroded outlines due to the 

 corrosive action of the invading rock : moreover, at the right-hand 

 end of the big block of norite shown in the photograph, there is 

 seen a rock of patchy character due to incomplete assimilation of 

 the fragments by coarse norite. (See p. 312.) 

 2. Beerbachite invading and incorporating normal norite^ 

 TVilberforce Spur. The photograph shows a large residual 

 boulder, about 6 feet long, consisting mainly of beerbachite ; on 

 the weathered siu-face may be seen irregular streaks and patches, 

 due to fragments of normal norite which have been softened, drawn 

 out. and partly incorporated by the beerbachite magma. (See 

 p. 315.) 



Plate XTni. 



Fig. 1. Normal norite [C 3], summit of Leicester Peak. A large 

 fresh crystal of olivine is cut by the lower end of the vertical wire, 

 and two crystals of schUlerized diallage are cut by the horizontal 

 wire ; hypersthene partly enwraps the olivine and diallage. The 

 clear mineral is labradorite. In the top left-hand quadrant is part 

 of a crystal of labradorite which is completely enclosed in diallage 

 and hypersthene ; the labradorite of the central part of the section 

 is later than the hypersthene. Several grains of iron- ore are 

 enclosed in hypersthene. Ordinary light. X 23. (See p. 32-5.) 



2. Beerbachite ~C 93], Wilberforce. The following minerals are 



present, mostly in granular form : — ^pyroxenes, chiefly hypersthene, 

 felsi^ar, and black iron-ore. Some of the pyroxenes possess idio- 

 morphic outlines. The minerals show a slight tendency to paral- 

 lehsm. Ordinary light. X 23. (See p. 326.) 



3. "Xorite-aplite ]C172a], near York. The photograph shows 



much fine micropegmatite and also two large crystals of acid 

 plagioclase, one of which possesses two sets of twin-lamellae inter- 

 secting at right angles. Small patches of felspar with twin striae 

 are enclosed in the micropegmatite. The plagioclase. as well as 

 the orthoclase,is seen to be graphically intergrown with the quartz. 

 At the intersection of the cross -wires is a fine spongy mass of 

 enstatite. and adjacent to it, in the lower right-hand quadrant, is 

 another mass which is of somewhat less dense texture ; the second 

 mass consists of minute, more or less parallel, prisms of enstatite, 

 all embedded in a plate of felspar which shows fine twin-lamellse.. 

 Crossed nicols. X 28. (See p. 322.) 



