﻿662 ME. J. A. HOWE PENOLOGICAL NOTES [Aug. I905, 



of hornblende occurs in a few patches. Biotite is present, but is 

 sparingly represented ; it is often greenish in colour. A little 

 sphene is associated with the mica. A few small rounded crystals 

 of zircon are present, also short prisms of apatite. (See 

 Pl.XLIII, fig. 2.) 



No. 33 (amphibolite). — A very dark-greenish rock of uniformly- 

 fine grain, speckled with small white spots of felspar. The foliation 

 is made evident by the orientation of the hornblende-crystals. 



Green hypidiomorphic crystals of hornblende make up the bulk 

 of the rock. The granular felspar is all quite fresh, and most of 

 it is plagioclase. Quartz is present, but is subordinate. 



Rocks from the Nile Valley, between Lado on the north 

 and Duflle on the south. 



With the exception of the basic dykes south of Redjaf (No. 22), all 

 the specimens from this area are either quartz-schists, mica-schists, 

 or microcline-gneisses. Specimens 38, 25, 43, 30, 26, 27, 28, 29, 

 23, & 24. 



No. 27, Mount Nieri (microcline-gneiss\ — A pinkish-grey banded 

 gneiss. The thin section exhibits a granitoid texture and somewhat 

 coarse grain. Quartz and orthoclastic felspar make up the bulk of 

 the rock, with flakes of muscovite roughly arranged in lines. The 

 quartz is fairly abundant; it extinguishes with strain-shadows. 

 The orthoclase is very fresh : Carlsbad-twinning is prevalent. In 

 places an older, muddy felspar occurs in small amount. Microcline 

 is present in fairly-high proportion, as well as some oligoclase; 

 all these minerals occur together in a coarser or finer granular 

 aggregate. A few grains of apatite are present. 



Nos. 25 & 30 from near Mudi ; also Nos. 26 & 28 from the 

 ridge north of Mount Nieri (quartz-schists and mica-schists). — These 

 are all examples of quartz-schists, passing by every intermediate 

 variation into micaceous quartz-schists. Nos. 25 & 30 are more 

 micaceous than the other two, and the latter is more micaceous 

 than the former. The foliation causes the rocks to break readily in 

 one direction ; the more quartzose forms have a very saccharoidal 

 appearance in the cross-fractures. 



No. 29, north of Mount Nieri, is a coarse, highly-micaceous gneiss. 



No. 38, from near Uando, is a cream-coloured gneiss. 



No. 22, dykes south of Eedjaf on the Nile (basic andesite). — 

 A black, even-textured rock. Felspar-laths with interstitial granular 

 augite, larger phenocrysts of anorthoclase, sometimes broken. 



There is one specimen from Suronga, a brownish chert, 

 which might have been of greater interest if it had been seen in situ 



