540 MR G. W. TYRRELL. 



and the almost exact correspondence of petrographic types, make the identity of the 

 two series even more certain. 



Rocks referable to three of the four divisions into which Holland divides the 

 charnockite series are to he found in this collection, as well as a rock which may be 

 described as a charnockite-porphyry. A rock comparable to charnockite in the narrow 

 sense is found to the W. of Ochilesa (177). It consists mainly of quartz, oligoclase, 

 orthoclase, with subordinate biotite, hypersthene, and monoclinic pyroxene. Both 

 quartz and orthoclase show strain-shadows, and the twinning of the oligoclase is often 

 discontinuous, wedging out in short distances and then reappearing. *The soda-lime 

 felspar is rather more abundant than in the Indian charnockite, and considerably ex- 

 ceeds the orthoclase in quantity (see Table I, l). The biotite occurs in large ragged 

 flakes, and is of a dark-brown, strongly pleochroic variety. Hypersthene is uniformly 

 distributed in typical irregular, prismatic, cross-fractured crystals, with distinct 

 pleochroism and faint lamellar twinning. There is also a pale-green monoclinic 

 pyroxene. This mineral appears in all stages of alteration to a fibrous amphibole 

 which has a distinct pleochroism from yellowish-green to a glaucophane-like blue. 

 The amphibole occasionally forms a narrow zone grown around the hypersthene 

 crystals. The texture of this rock is not so thoroughly granulitic as in the more 

 basic rocks of the series. It may be described as intermediate between granitic and 

 granulitic. In the hand specimen this rock has a distinct gneissic banding, which is, 

 however, not apparent in thin section. 



A rock from the N. of Etunda (193) is referable to Holland's intermediate 

 division of the charnockite series. Compared with the foregoing, quartz and ortho- 

 clase have so diminished in quantity as to become merely interstitial to the abundant 

 plagioclase, whilst the amount of ferro-magnesian minerals remains stationary. 

 Magnetite shows a large increase (see Table I, 2). Monoclinic pyroxene does not 

 appear in this rock. The hypersthene is thoroughly anhedral, and has an intense 

 pleochroism from pink to bluish-green. The rock also contains a little pink garnet 

 which forms the centres of irregular aggregates of hypersthene and biotite. There is 

 a tendency for the ferro-magnesian minerals to segregate into narrow linear areas, 

 giving rise to a rude banding.* The water-clear plagioclase is richer in the anorthite 

 molecule than in the charnockite proper, and is an andesine of composition Ab4An3. 

 The texture of this rock is thoroughly granulitic. Its normal eruptive equivalent 

 would probably be called quartz-mica-hypersthene-diorite or quartz-mica-norite. 

 From the district S. of Andulo (194«), and from Ochilesa (1766), come rocks 

 strictly comparable with those called " hornblende-augite-norite " by Holland.! 

 These are ideally fresh rocks consisting of a thoroughly granulitic aggregate of water- 

 clear plagioclase (A.b]Ani) with pale-green augite, hypersthene, hornblende, iron-ores, 

 and a little biotite. In the rock from Andulo (194a) the hornblende is a brownish- 



* Of. " Charnockite of the Ivory Coast," Lacroix, Comptea Kendus, cl (1910), p. 20. 

 t Holland, op. cit., p. 157. 



