DESCRIPTION OF SECTIONS. 245 



From Balanosh Zicirat westwards I did not examine the hills for 



Rocks east and south- about nft y miles - J ud g in S from fragments 

 east of Pushtiwan. carried down by rivers, they seem to consist 



principally of basic and acid igneous rocks just as near Chigai. 

 When encamped at Mirui I visited them in the neighbourhood of 

 li Pushtiwan/' They are separated from the Mirui hills by a pebble- 

 strewn plain in the midst of which there rise some sedimentary 

 strata with a southerly dip, south of Tahlab Well. East of Tahlab 

 Well there outcrops some diorite, north of which we find great masses 

 of basic rocks apparently intrusive, and again north of this a con- 

 siderable outcrop of quartz-diorite. This rock which, in the field 

 especially, has quite a granitic appearance is very rich in quartz and 

 does not seem to contain any orthoclase. The constituent minerals 

 are plagioclase, quartz, hornblende/biotite and magnetite. The appear- 

 ance of the rock varies greatly within short distances owing to the 

 varying proportions of the above minerals. One variety which in the 

 field has the appearance of an aplite consists of nothing but quartz 

 and plagioclase felspar. When microscopic sections of the rock are 

 examined it is found that the structure is seldom truly granitic, but 

 has everywhere a most distinct tendency towards that of a grano- 

 phyre. The coarseness of grain varies as much as the composition 

 of the rock, and it is a fact worthy of notice that at its junction with 

 the basic rocks, the diorite becomes a felsite consisting of porphyritic 

 crystals of quartz and of felspar distributed through a minutely 

 microcrystalline groundmass. In this special case therefore the acid 

 rock seems newer than the basic one, for the basic one had already 

 cooled down when the dioritic intrusion took place. Thus, judging 

 from this one fact alone, the quartz-diorite may be regarded as one of 

 those intrusions which are at the oldest of upper eocene age, as was 

 pointed out in a previous chapter (page 23) just like the Ra"s K6h 

 intrusion and others. Yet there are circumstances which make them 

 appear much more directly connected with the volcanic products of 

 the flysch period in this present instance. One of them is the presence 

 of micropegmatite not only in small masses with porphyritic structure 



F2 .( 67 ) 



