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and Llmenite. The hornblende- 

 gneisses and pyroxene-granite 

 enclose small pockets of caleite, 

 and near the boundaries of the 

 crystalline limestone many in- 

 teresting contact-minerals are 

 developed. The hornblende- 

 gneisses pass imperceptibly into 

 the surrounding biotite-gneiss 

 and are almost certainly of the 

 same age, the incoming of horn- 

 blende and plagioclase being 

 attributed to interchange of 

 material between the biotite- 

 gneiss and che crystalline lime- 

 stone. According to this reading 

 the succession in order of age is 

 (a) crystalline limestone (fors- 

 terite-marble), (b) biotite- and 

 hornblende-gneisses, (c) pyro- 

 xene-granite, (d) graphic granite 

 and other pegmatites. At the 

 junction of the river and the 

 road, a dark compact pierite-dyke 

 about 10 feet thick appears on 

 the right-hand side of the river- 

 bed, and crosses obliquely to the 

 other bank, taking a north-north- 

 westerly to south-south-easterly 

 direction across the strike of the 

 older rocks. The Ampwihi makes 

 a sudden bend about 70 yards 

 to the south-east so that it re- 

 turns towards the dyke, which 

 is again exposed across its sandy 

 floor. The dyke is clearly the 

 latest rock of the district, and is 

 intruded along a line of fault — 

 for in two cases pegmatite-dykes 

 seen on the eastern side are 

 broken across, and reappear on 

 the western side with a well- 

 marked northward displacement. 1 

 On the northern slopes of the 

 Monapo Valley, south-east of 

 Mount Tibwi/ the late R. L. 

 Reid found a large mass of nearly 

 pure crystalline limestone, em- 

 bedded in hornblende-biotite- 

 gneiss and intruded upon by 

 muscovite-bearing pegmatites. 



1 A. Holmes, Geol. Mag. dec. G, 

 vol. iv (1917) p. 150. 



